API
Modules
Types and constants
Functions and macros
LegendSpecFits.LQ_cut
LegendSpecFits._fit_fwhm_ft
LegendSpecFits._fit_fwhm_ft_ctc
LegendSpecFits._get_model_counts
LegendSpecFits._prepare_data
LegendSpecFits.advanced_time_and_memory_control
LegendSpecFits.aoe_compton_background_peakshape
LegendSpecFits.aoe_compton_peakshape
LegendSpecFits.aoe_compton_peakshape_components
LegendSpecFits.aoe_compton_signal_peakshape
LegendSpecFits.array_to_tuple
LegendSpecFits.autocal_energy
LegendSpecFits.background_peakshape
LegendSpecFits.baseline_qc
LegendSpecFits.chi2fit
LegendSpecFits.ctc_energy
LegendSpecFits.cut_single_peak
LegendSpecFits.double_gaussian
LegendSpecFits.estimate_combined_peak_stats
LegendSpecFits.estimate_fwhm
LegendSpecFits.estimate_single_peak_stats
LegendSpecFits.ex_gauss_pdf
LegendSpecFits.ex_step_gauss
LegendSpecFits.expand_vars
LegendSpecFits.exponential_decay
LegendSpecFits.fit_aoe_compton
LegendSpecFits.fit_aoe_compton_combined
LegendSpecFits.fit_aoe_corrections
LegendSpecFits.fit_binned_double_gauss
LegendSpecFits.fit_binned_trunc_gauss
LegendSpecFits.fit_calibration
LegendSpecFits.fit_enc_sigmas
LegendSpecFits.fit_fwhm
LegendSpecFits.fit_fwhm_ft
LegendSpecFits.fit_half_centered_trunc_gauss
LegendSpecFits.fit_half_trunc_gauss
LegendSpecFits.fit_lq_compton
LegendSpecFits.fit_peaks
LegendSpecFits.fit_peaks_combined
LegendSpecFits.fit_sf_wl
LegendSpecFits.fit_single_aoe_compton
LegendSpecFits.fit_single_aoe_compton_with_fixed_μ_and_σ
LegendSpecFits.fit_single_lq_compton
LegendSpecFits.fit_single_peak_th228
LegendSpecFits.fit_single_trunc_gauss
LegendSpecFits.fit_sipm_spectrum
LegendSpecFits.fit_subpeaks_th228
LegendSpecFits.gamma_peakshape
LegendSpecFits.gauss_pdf
LegendSpecFits.generate_aoe_compton_bands
LegendSpecFits.get_centered_gaussian_window_cut
LegendSpecFits.get_continuum_survival_fraction
LegendSpecFits.get_distribution_transform
LegendSpecFits.get_friedman_diaconis_bin_width
LegendSpecFits.get_low_aoe_cut
LegendSpecFits.get_mc_value_shapes
LegendSpecFits.get_mc_value_shapes
LegendSpecFits.get_number_of_bins
LegendSpecFits.get_peak_fwhm_th228
LegendSpecFits.get_peak_survival_fraction
LegendSpecFits.get_peakhists_th228
LegendSpecFits.get_peaks_survival_fractions
LegendSpecFits.get_residuals
LegendSpecFits.get_sf_after_aoe_cut
LegendSpecFits.get_th228_fit_functions
LegendSpecFits.highEtail_peakshape
LegendSpecFits.hist_loglike
LegendSpecFits.linear_function
LegendSpecFits.lowEtail_peakshape
LegendSpecFits.lq_drift_time_correction
LegendSpecFits.nearestSPD
LegendSpecFits.p_value
LegendSpecFits.p_value_MC
LegendSpecFits.p_value_poissonll
LegendSpecFits.peak_centroid
LegendSpecFits.peakshape_components
LegendSpecFits.prepare_sep_peakhist
LegendSpecFits.pulser_cal_qc
LegendSpecFits.set_memlimit
LegendSpecFits.set_timelimit
LegendSpecFits.signal_peakshape
LegendSpecFits.simple_calibration
LegendSpecFits.sipm_simple_calibration
LegendSpecFits.step_gauss
LegendSpecFits.subhist
LegendSpecFits.tuple_to_array
LegendSpecFits.weibull_from_mx
Documentation
LegendSpecFits.LegendSpecFits
— ModuleLegendSpecFits
Template for Julia packages.
LegendSpecFits.LQ_cut
— MethodDEP_µ::Unitful.Energy, DEP_σ::Unitful.Energy, e_cal::Vector{<:Unitful.Energy}, lq_classifier::Vector{Float64}; cut_sigma::Float64=3.0, truncation_sigma::Float64=2.0)
Evaluates the cutoff value for the LQ cut. The function performs a binned gaussian fit on the sidebandsubtracted LQ histogram and evaluates the cutoff value difined at 3σ of the fit.
Returns
* `result`: NamedTuple of the cutoff value
* `report`: NamedTuple of the fit result, fit report and temporary histograms
LegendSpecFits._fit_fwhm_ft
— Method_fit_fwhm_ft(e_grid::Matrix, e_grid_ft::StepRangeLen{Quantity{<:T}, Base.TwicePrecision{Quantity{<:T}}, Base.TwicePrecision{Quantity{<:T}}, Int64}, rt::Unitful.RealOrRealQuantity, min_e::T, max_e::T, nbins::Int64, rel_cut_fit::T; default_ft::Quantity{T}=3.0u"µs", ft_fwhm_tol::Unitful.Energy{<:Real} = 0.1u"keV") where {T <:Real}
Fit the FWHM values in e_grid
for each FT in e_grid_ft
with a Gamma Peakshape and return the optimal FT and the corresponding FWHM value. The cut values cut for each flat-top time a window for better histogramming.
Arguments
e_grid
: 2D array of energy values for each FT ine_grid_ft
e_grid_ft
: 1D array of FT values for which the FWHM values ine_grid
are calculatedrt
: RT value for which the FWHM values ine_grid
are calculatedmin_e
: minimum energy value to consider for the fitmax_e
: maximum energy value to consider for the fitnbins
: number of bins to use for the histogram of energy valuesrel_cut_fit
: relative cut value to use for the fitft_fwhm_tol
: search for lowest "optimal" ft withinminimum(fwhm) + ft_fwhm_tol
to avoid artificially large ft
Returns
ft
: optimal FT valuemin_fwhm
: corresponding FWHM value
LegendSpecFits._fit_fwhm_ft_ctc
— Method_fit_fwhm_ft_ctc(e_grid::Matrix, e_grid_ft::StepRangeLen, qdrift::Vector{<:Real}, rt::Unitful.RealOrRealQuantity, min_e::T, max_e::T, nbins::Int64, rel_cut_fit::T; default_ft::Quantity{T}=3.0u"µs", peak::Unitful.Energy{<:Real}=2614.5u"keV", window::Tuple{<:Unitful.Energy{<:Real}, <:Unitful.Energy{<:Real}}=(35.0u"keV", 25.0u"keV"), ft_fwhm_tol::Unitful.Energy{<:Real} = 0.1u"keV") where {T <:Real}
Fit the FWHM values in e_grid
for each FT in e_grid_ft
with a Gamma Peakshape and return the optimal FT and the corresponding FWHM value. The cut values cut for each flat-top time a window for better histogramming.
Arguments
e_grid
: 2D array of energy values for each FT ine_grid_ft
e_grid_ft
: 1D array of FT values for which the FWHM values ine_grid
are calculatedqdrift
: drift time values for each energy value ine_grid
rt
: RT value for which the FWHM values ine_grid
are calculatedmin_e
: minimum energy value to consider for the fitmax_e
: maximum energy value to consider for the fitnbins
: number of bins to use for the histogram of energy valuesrel_cut_fit
: relative cut value to use for the fitft_fwhm_tol
: search for lowest "optimal" ft withinminimum(fwhm) + ft_fwhm_tol
to avoid artificially large ft
Returns
ft
: optimal FT valuemin_fwhm
: corresponding FWHM value
LegendSpecFits._get_model_counts
— Method_get_model_counts(f_fit::Base.Callable,v_ml::Union{NamedTuple, AbstractVector},bin_centers::StepRangeLen,bin_widths::StepRangeLen)
aux. function to get modelled peakshape based on histogram binning and best-fit parameter
LegendSpecFits._prepare_data
— Method_prepare_data(h::Histogram{<:Real,1})
aux. function to convert histogram data into bin edges, bin width and bin counts
LegendSpecFits.advanced_time_and_memory_control
— Methodadvanced_time_and_memory_control(x::Optim.OptimizationState, start_time::Float64, time_to_setup::Float64; time_limit::Float64=60.0, mem_limit::Float64=30.0)
Control function to stop optimization based on time and memory usage.
Arguments
x::Optim.OptimizationState
: optimization statestart_time::Float64
: start timetime_to_setup::Float64
: time to setuptime_limit::Float64
: time limitmem_limit::Float64
: memory limit
Return
Bool
: true if optimization should stop
LegendSpecFits.aoe_compton_background_peakshape
— Methodaoe_compton_background_peakshape(
x::Real, μ::Real, σ::Real,
background::Real, δ::Real
)
Describes the background shape of a typical A/E Compton peak in a detector as a step like background for MSE events.
LegendSpecFits.aoe_compton_peakshape
— Methodaoe_compton_peakshape(
x::Real, μ::Real, σ::Real, n::Real,
background::Real, δ::Real
)
Describes the shape of a typical A/E Compton peak in a detector as a gaussian SSE peak and a step like background for MSE events.
LegendSpecFits.aoe_compton_peakshape_components
— Methodaoe_compton_peakshape_components(fit_func::Symbol; background_center::Real)
This function defines the components (signal, low/high-energy tail, backgrounds) of the fit function used in gamma specfits. These component functions are used in the fit-report and in plot receipes
LegendSpecFits.aoe_compton_signal_peakshape
— Methodaoe_compton_signal_peakshape(
x::Real, μ::Real, σ::Real, n::Real
)
Describes the signal shape of a typical A/E Compton peak in a detector as a gaussian SSE peak.
LegendSpecFits.array_to_tuple
— Methodarray_to_tuple(a::AbstractArray, as_nt::NamedTuple)
Return a NamedTuple
with the values of a
in the order given by fieldnames(as_nt)
.
LegendSpecFits.autocal_energy
— Methodautocal_energy(e::AbstractArray{<:Real}, photon_lines::Vector{<:Unitful.RealOrRealQuantity}; min_e::Real=100, max_e_binning_quantile::Real=0.5, σ::Real = 2.0, threshold::Real = 50.0, min_n_peaks::Int = length(photon_lines), max_n_peaks::Int = 4 * length(photon_lines), α::Real = 0.01, rtol::Real = 5e-3)
Compute an energy calibration from raw reconstructed energy deposition values based on a given number of known photon lines which are contained in the spectrum
LegendSpecFits.background_peakshape
— Methodbackground_peakshape(
x::Real, μ::Real, σ::Real,
step_amplitude::Real, background::Real;
background_slope::Real = 0.0, background_exp = 0.0, background_center::Real = µ
)
Describes the background part of the shape of a typical gamma peak in a detector: components:
- step-function scaled with
step_amplitude
` - energy-independent background:
background
` - linear slope:
background_slope
(optional) - exponential decay:
background_exp
(optional)
LegendSpecFits.baseline_qc
— Methodbaseline_qc(data, qc_config)
Perform simple Gaussian fits on the baseline disitrbutions for a given data set.
Returns
result
: Namedtuple containing the cut and fit results for each baseline variablereport
: Namedtuple containing plotable objects.
LegendSpecFits.chi2fit
— Methodfit_chisq(x::AbstractVector{<:Real},y::AbstractVector{<:Real},yerr::AbstractVector{<:Real}, f_fit::Function;pull_t::Vector{<:NamedTuple} = fill(NamedTuple(), first(methods(f_fit)).nargs - 2), v_init::Vector = [])
Least square fit with chi2 minimization
Input:
- x : x-values
- y : y-values
- yerr : 1 sigma uncertainty on y
- ffit : fit/model function. e.g. for a linear function: flin(x,p1,p2) = p1 .* x .+ p2
The numer of fit parameter is determined with first(methods(f_fit)).nargs - 2
. That's why it's important that ffit has the synthax f(x,arg1,arg2,arg3,...) pullt : pull term, a vector of NamedTuple with fields mean
and std
. A Gaussian pull term is added to the chi2 function to account for systematic uncertainties. If left blank, no pull term is used. v_init : initial value for fit parameter optimization. If left blank, the initial value is set to 1 or guessed roughly for all fit parameters
Return:
- result : NamedTuple with the optimized fit parameter and the fit function
- report:
LegendSpecFits.ctc_energy
— Functionctc_energy(e::Array{T}, qdrift::Array{T}, peak::T, window::T) where T<:Real
Correct for the drift time dependence of the energy by minimizing the ratio of the FWHM and the peak height of the peak around peak
in e
with a cut window of window
. The drift time dependence is given by qdrift
.
Returns
* `peak`: peak position
* `window`: window size
* `fct`: correction factor
* `fwhm_before`: FWHM before correction
* `fwhm_after`: FWHM after correction
* `func`: function to correct energy
* `func_generic`: generic function to correct energy
LegendSpecFits.cut_single_peak
— Methodcut_single_peak(x::Array, min_x::Float64, max_x::Float64,; n_bins::Int=-1, relative_cut::Float64=0.5)
Cut out a single peak from the array x
between min_x
and max_x
. The number of bins is the number of bins to use for the histogram. The relative cut is the fraction of the maximum counts to use for the cut.
Returns
* `max`: maximum position of the peak
* `low`: lower edge of the cut peak
* `high`: upper edge of the cut peak
LegendSpecFits.double_gaussian
— Methoddouble_gaussian(
x::Real, μ1::Real, σ1::Real, n1::Real,
μ2::Real, σ2::Real, n2::Real
)
Evaluates the sum of two gaussians at x
with parameters μ1
, σ1
, n1
, μ2
, σ2
, n2
.
LegendSpecFits.estimate_combined_peak_stats
— Methodestimate_combined_peak_stats(peakstats::StructArray,; calib_type::Symbol=:th228)
Estimate the peak position, FWHM, sigma, counts and background of a peak from a histogram.
LegendSpecFits.estimate_fwhm
— Methodestimate_fwhm(v::NamedTuple, v_err::NamedTuple)
Get the FWHM of a peak from the fit parameters.
Returns
* `fwhm`: the FWHM of the peak
LegendSpecFits.estimate_single_peak_stats
— Methodestimate_single_peak_stats(h::Histogram, calib_type::Symbol=:th228)
Estimate statistics/parameters for a single peak in the given histogram h
.
h
must only contain a single peak. The peak should have a Gaussian-like shape. calib_type
specifies the calibration type. Currently :th228
, :psd
and :simple
is implemented..
Returns
NamedTuple
with the fields * peak_pos
: estimated position of the peak (in the middle of the peak) * peak_fwhm
: full width at half maximum (FWHM) of the peak * peak_sigma
: estimated standard deviation of the peak * peak_counts
: estimated number of counts in the peak * mean_background
: estimated mean background value
LegendSpecFits.ex_gauss_pdf
— Methodex_gauss_pdf(x::Real, μ::Real, σ::Real, θ::Real)
The PDF of an Exponentially modified Gaussian distribution with Gaussian parameters μ
, σ
and exponential scale θ
at x
.
It is the PDF of the distribution that descibes the random process rand(Normal(μ, σ)) + rand(Exponential(θ))
.
LegendSpecFits.ex_step_gauss
— Methodex_step_gauss(x::Real, l::Real, k::Real, t::Real, d::Real)
Evaluates an extended step gauss model at x
with parameters l
, k
, t
and d
.
LegendSpecFits.expand_vars
— Methodexpand_vars(v::NamedTuple)::StructArray
Expand all fields in v
(scalars or arrays) to same array size and return a StructArray
.
LegendSpecFits.exponential_decay
— Methodexponential_decay(x::Real, amplitude::Real, decay::Real, offset::Real)
Evaluates an exponential decay function at x
with parameters amplitude
, decay
and offset
.
LegendSpecFits.fit_aoe_compton
— Methodfit_aoe_compton(peakhists::Array, peakstats::StructArray, compton_bands::Array{T}) where T<:Real
Fit the A/E Compton bands using the f_aoe_compton
function consisting of a gaussian SSE peak and a step like background for MSE events.
Returns
* `result`: Dict of NamedTuples of the fit results containing values and errors for each compton band
* `report`: Dict of NamedTuples of the fit report which can be plotted for each compton band
LegendSpecFits.fit_aoe_compton_combined
— Methodfit_aoe_compton_combined(peakhists::Vector{<:Histogram}, peakstats::StructArray, compton_bands::Array{T}, result_corrections::NamedTuple; pars_aoe::NamedTuple{(:μ, :μ_err, :σ, :σ_err)}=NamedTuple{(:μ, :μ_err, :σ, :σ_err)}(nothing, nothing, nothing, nothing), uncertainty::Bool=false) where T<:Unitful.Energy{<:Real}
Performed a combined fit over all A/E Compton band using the f_aoe_compton
function consisting of a gaussian SSE peak and a step like background for MSE events, assuming f_aoe_mu
for μ
and f_aoe_sigma
for σ
.
Returns
* `v_ml`: The fit result from the maximum-likelihood fit.
* `report_μ`: Report to plot the combined fit result for the enery-dependence of `μ`.
* `report_σ`: Report to plot the combined fit result for the enery-dependence of `σ`.
* `report_bands`: Dict of NamedTuples of the fit report which can be plotted for each compton band
LegendSpecFits.fit_aoe_corrections
— Methodfitaoecorrections(e::Array{<:Unitful.Energy{<:Real}}, μ::Array{<:Real}, σ::Array{<:Real})
Fit the corrections for the AoE value of the detector.
Returns
e
: Energy valuesμ
: Mean valuesσ
: Sigma valuesμ_scs
: Fit result for the mean valuesf_μ_scs
: Fit function for the mean valuesσ_scs
: Fit result for the sigma valuesf_σ_scs
: Fit function for the sigma values
LegendSpecFits.fit_binned_double_gauss
— Methodfit_binned_double_gauss(h::Histogram, ps::NamedTuple{(:peak_pos, :peak_fwhm, :peak_sigma, :peak_counts, :mean_background, :μ, :σ), NTuple{7, T}}; uncertainty::Bool=true) where T<:Real
Perform a binned fit of the peakshape to the data in h
using the initial values in ps
while using the f_double_gauss
function consisting of a double gaussian peak. The priors for the first gaussian peak are given by the ps
tuple. For the priors of the second gaussian peak a wide window around the first peak is used.
Returns
* `result`: NamedTuple of the fit results containing values and errors
* `report`: NamedTuple of the fit report which can be plotted
LegendSpecFits.fit_binned_trunc_gauss
— Methodfit_binned_trunc_gauss(h::Histogram, ps::NamedTuple{(:peak_pos, :peak_fwhm, :peak_sigma, :peak_counts, :mean_background, :μ, :σ), NTuple{7, T}}; uncertainty::Bool=true) where T<:Real
Perform a binned fit of the peakshape to the data in h
using the initial values in ps
while using the f_gauss
function consisting of a gaussian peak multiplied with an amplitude n.
Returns
* `result`: NamedTuple of the fit results containing values and errors
* `report`: NamedTuple of the fit report which can be plotted
LegendSpecFits.fit_calibration
— Methodfit_calibration(pol_order::Int, µ::AbstractVector{<:Union{Real,Measurement{<:Real}}}, peaks::AbstractVector{<:Union{Real,Measurement{<:Real}}}; pull_t::Vector{<:NamedTuple}=fill(NamedTuple(), pol_order+1), v_init::Vector = [], uncertainty::Bool=true )
Fit the calibration lines with polynomial function of polorder order polorder == 1 -> linear function pol_order == 2 -> quadratic function
Returns
* `result`: NamedTuple with the following fields
* `par`: best-fit parameters
* `gof`: godness of fit
* `report`:
LegendSpecFits.fit_enc_sigmas
— Methodfit_enc_sigmas(enc_grid::Matrix{T}, enc_grid_rt::StepRangeLen{Quantity{<:T}, Base.TwicePrecision{Quantity{<:T}}, Base.TwicePrecision{Quantity{<:T}}, Int64}, min_enc::T, max_enc::T, nbins::Int64, rel_cut_fit::T) where T<:Real
Fit the ENC values in enc_grid
for each RT in enc_grid_rt
with a Gaussian and return the optimal RT and the corresponding ENC value.
Arguments
enc_grid
: 2D array of ENC values for each RT inenc_grid_rt
enc_grid_rt
: 1D array of RT values for which the ENC values inenc_grid
are calculatedmin_enc
: minimum ENC value to consider for the fitmax_enc
: maximum ENC value to consider for the fitnbins
: number of bins to use for the histogram of ENC valuesrel_cut_fit
: relative cut value to use for the fit
Returns
rt
: optimal RT valuemin_enc
: corresponding ENC value
LegendSpecFits.fit_fwhm
— FunctionfitFWHM(fit_fwhm(peaks::Vector{T}, fwhm::Vector{T}) where T<:Real
Fit the FWHM of the peaks to a quadratic function.
Returns
* `qbb`: the FWHM at 2039 keV
* `err`: the uncertainties of the fit parameters
* `v`: the fit result parameters
* `f_fit`: the fitted function
LegendSpecFits.fit_fwhm_ft
— Methodfit_fwhm_ft(e_grid::Matrix, e_grid_ft::StepRangeLen, rt::Unitful.RealOrRealQuantity, min_e::T, max_e::T, rel_cut_fit::T, apply_ctc::Bool=true; kwargs...)
fit_fwhm_ft(e_grid::Matrix, e_grid_ft::StepRangeLen, rt::Unitful.RealOrRealQuantity, min_e, max_e, rel_cut_fit; kwargs...)
fit_fwhm_ft(e_grid::Matrix, e_grid_ft::StepRangeLen, qdrift::Vector{<:Real}, rt::Unitful.RealOrRealQuantity, min_e, max_e, rel_cut_fit; kwargs...)
Fit the FWHM values in e_grid
for each FT in e_grid_ft
with a Gamma Peakshape and return the optimal FT and the corresponding FWHM value. The cut values cut for each flat-top time a window for better histogramming. If the apply_ctc
flag is set to true
, the CTC correction is applied to the energy values. Othwise, if a qdrift
vector is provided, the CTC correction is applied to the energy values.
Arguments
e_grid
: 2D array of energy values for each FT ine_grid_ft
e_grid_ft
: 1D array of FT values for which the FWHM values ine_grid
are calculatedrt
: RT value for which the FWHM values ine_grid
are calculatedmin_e
: minimum energy value to consider for the fitmax_e
: maximum energy value to consider for the fitrel_cut_fit
: relative cut value to use for the fit
Returns
ft
: optimal FT valuemin_fwhm
: corresponding FWHM value
LegendSpecFits.fit_half_centered_trunc_gauss
— Methodfit_half_centered_trunc_gauss(x::Array, cuts::NamedTuple{(:low, :high, :max), Tuple{Float64, Float64, Float64}})
Fit a single truncated Gaussian to the data x
between cut.low
and cut.high
. The peak center is fixed at μ
and the peak is cut in half either in the left or right half.
Returns report
and result
` with:
* `f_fit`: fitted function
* `μ`: mean of the Gaussian
* `σ`: standard deviation of the Gaussian
LegendSpecFits.fit_half_trunc_gauss
— Methodfit_half_trunc_gauss(x::Array, cuts::NamedTuple{(:low, :high, :max), Tuple{Float64, Float64, Float64}})
Fit a single truncated Gaussian to the data x
between cut.low
and cut.high
. The peak center is fixed at μ
and the peak is cut in half either in the left or right half.
Returns report
and result
with:
* `f_fit`: fitted function
* `μ`: mean of the Gaussian
* `σ`: standard deviation of the Gaussian
LegendSpecFits.fit_lq_compton
— Methodfit_lq_compton(peakhists::Array, peakstats::StructArray, compton_bands::Array{T}) where T<:Real
Fit the A/E Compton bands using the f_lq_compton
function consisting of a gaussian SSE peak and a step like background for MSE events.
Returns
* `result`: Dict of NamedTuples of the fit results containing values and errors for each compton band
* `report`: Dict of NamedTuples of the fit report which can be plotted for each compton band
LegendSpecFits.fit_peaks
— Methodfit_peaks(peakhists::Array, peakstats::StructArray, th228_lines::Array,; calib_type::Symbol=:th228, uncertainty::Bool=true, low_e_tail::Bool=true)
Perform a fit of the peakshape to the data in peakhists
using the initial values in peakstats
to the calibration lines in th228_lines
.
Returns
* `peak_fit_plots`: array of plots of the peak fits
* `return_vals`: dictionary of the fit results
LegendSpecFits.fit_peaks_combined
— Methodfit_peaks_combined(peakhists::Array, peakstats::StructArray, th228_lines::Array{T},; calib_type::Symbol=:th228, uncertainty::Bool=true, fixed_position::Bool=false) where T<:Real
Fit the peaks of a histogram to a combined peakshape function while sharring parameters between peaks.
LegendSpecFits.fit_sf_wl
— Methodfit_sf_wl(dep_sep_data, a_grid_wl_sg, optimization_config)
Fit a A/E filter window length for the SEP data and return the optimal window length and the corresponding survival fraction.
Arguments
dep_sep_data
: NamedTuple with the DEP and SEP dataa_grid_wl_sg
: range of window lengths to sweep throughoptimization_config
: configuration dictionary
Returns
result
: optimal window length and corresponding survival fractionreport
: report with all window lengths and survival fractions
LegendSpecFits.fit_single_aoe_compton
— Methodfit_single_aoe_compton(h::Histogram, ps::NamedTuple{(:peak_pos, :peak_fwhm, :peak_sigma, :peak_counts, :mean_background, :μ, :σ), NTuple{7, T}}; uncertainty::Bool=true) where T<:Real
Perform a fit of the peakshape to the data in h
using the initial values in ps
while using the f_aoe_compton
function consisting of a gaussian SSE peak and a step like background for MSE events.
Returns
* `result`: NamedTuple of the fit results containing values and errors
* `report`: NamedTuple of the fit report which can be plotted
LegendSpecFits.fit_single_aoe_compton_with_fixed_μ_and_σ
— Methodfit_single_aoe_compton_with_fixed_μ_and_σ(h::Histogram, μ::Number, σ::Number, ps::NamedTuple; uncertainty::Bool=true)
Fit a single A/E Compton band using the f_aoe_compton
function consisting of a gaussian SSE peak and a step like background for MSE events using fixed values for μ and σ.
Returns
* `neg_log_likelihood`: The negative log-likelihood of the likelihood fit
* `report`: Dict of NamedTuples of the fit report which can be plotted for each compton band
LegendSpecFits.fit_single_lq_compton
— Methodfit_single_lq_compton(h::Histogram, ps::NamedTuple{(:peak_pos, :peak_fwhm, :peak_sigma, :peak_counts, :mean_background, :μ, :σ), NTuple{7, T}}; uncertainty::Bool=true) where T<:Real
Perform a fit of the peakshape to the data in h
using the initial values in ps
while using the f_lq_compton
function consisting of a gaussian SSE peak and a step like background for MSE events.
Returns
* `result`: NamedTuple of the fit results containing values and errors
* `report`: NamedTuple of the fit report which can be plotted
LegendSpecFits.fit_single_peak_th228
— Methodfit_single_peak_th228(h::Histogram, ps::NamedTuple{(:peak_pos, :peak_fwhm, :peak_sigma, :peak_counts, :mean_background), NTuple{5, T}};, uncertainty::Bool=true, fixed_position::Bool=false, low_e_tail::Bool=true) where T<:Real
Perform a fit of the peakshape to the data in h
using the initial values in ps
while using the gamma_peakshape
with low-E tail. Also, FWHM is calculated from the fitted peakshape with MC error propagation. The peak position can be fixed to the value in ps
by setting fixed_position=true
. If the low-E tail should not be fitted, it can be disabled by setting low_e_tail=false
.
Returns
* `result`: NamedTuple of the fit results containing values and errors
* `report`: NamedTuple of the fit report which can be plotted
LegendSpecFits.fit_single_trunc_gauss
— Methodfit_single_trunc_gauss(x::Array, cuts::NamedTuple{(:low, :high, :max), Tuple{Float64, Float64, Float64}})
Fit a single truncated Gaussian to the data x
between min_x
and max_x
. Returns report
and result
with: *
ffit: fitted function *
μ: mean of the Gaussian *
μerr: error of the mean *
σ: standard deviation of the Gaussian *
σ_err: error of the standard deviation *
n`: number of counts in the peak
LegendSpecFits.fit_sipm_spectrum
— Functionfit_sipm_spectrum(pe_cal::Vector{<:Real}, min_pe::Real=0.5, max_pe::Real=3.5;
n_mixtures::Int=ceil(Int, (max_pe - min_pe) * 4), nIter::Int=50, nInit::Int=50,
method::Symbol=:kmeans, kind=:diag, Δpe_peak_assignment::Real=0.3, f_uncal::Function=identity, uncertainty::Bool=true)
Fit a Gaussian Mixture Model to the given pe calibration data and return the fit parameters.
Arguments
pe_cal::Vector{<:Real}
: the pe calibration datamin_pe::Real=0.5
: the minimum pe to considermax_pe::Real=3.5
: the maximum pe to considern_mixtures::Int=ceil(Int, (max_pe - min_pe) * 4)
: the number of mixtures to fitnIter::Int=50
: the number of iterations for the EM algorithmnInit::Int=50
: the number of initializations for the EM algorithmmethod::Symbol=:kmeans
: the method to use for initializationkind::Symbol=:diag
: the kind of covariance matrix to useΔpe_peak_assignment::Real=0.3
: the range to consider for peak assignmentf_uncal::Function=identity
: the function to use for uncalibrationuncertainty::Bool=true
: whether to calculate the uncertainty
Returns
result
: a tuple with the fit parametersreport
: a tuple with the fit report which can be plotted via a recipe
LegendSpecFits.fit_subpeaks_th228
— Methodfit_single_peak_th228(h::Histogram, ps::NamedTuple{(:peak_pos, :peak_fwhm, :peak_sigma, :peak_counts, :mean_background), NTuple{5, T}};, uncertainty::Bool=true, fixed_position::Bool=false, low_e_tail::Bool=true) where T<:Real
Perform a simultaneous fit of two peaks (h_survived
and h_cut
) that together would form a histogram h
, from which the result h_result
was already determined using fit_single_peak_th228
. Also, FWHM is calculated from the fitted peakshape with MC error propagation. The peak position can be fixed to the value in ps
by setting fixed_position=true
. If the low-E tail should not be fitted, it can be disabled by setting low_e_tail=false
.
Returns
* `result`: NamedTuple of the fit results containing values and errors, in particular the signal survival fraction `sf` and the background survival frachtion `bsf`.
* `report`: NamedTuple of the fit report which can be plotted
LegendSpecFits.gamma_peakshape
— Methodgamma_peakshape(
x::Real, μ::Real, σ::Real, n::Real,
step_amplitude::Real, skew_fraction::Real, skew_width::Real,
background::Real;
skew_fraction_highE::Real = 0.0, skew_width_highE::Real= 0.0,
background_kwargs...
)
Standard gamma peakshape: Describes the shape of a typical gamma peak in a detector. Components:
- Gaussian signal peak with
μ
,σ
,n - skew_fraction - skew_fraction_highE
- low-energy tail:
skew_fraction
,skew_width
- high-energy tail:
skew_fraction_highE
,skew_width_highE
(optional, default off) - background:
- energy-independent
background
- step-function scaled with
step_amplitude
from Compton scattered gammas - linear slope:
background_slope
(optional, default off) - exponential decay:
background_exp
(optional, default off)
- energy-independent
LegendSpecFits.gauss_pdf
— MethodLegendSpecFits.gauss_pdf(x::Real, μ::Real, σ::Real)
Equivalent to pdf(Normal(μ, σ), x)
LegendSpecFits.generate_aoe_compton_bands
— Methodgenerate_aoe_compton_bands(aoe::Vector{<:Real}, e::Vector{<:T}, compton_bands::Vector{<:T}, compton_window::T) where T<:Unitful.Energy{<:Real}
Generate histograms for the A/E Compton bands and estimate peak parameters. The compton bands are cutted out of the A/E spectrum and then binned using the Freedman-Diaconis Rule. For better performance the binning is only done in the area around the peak. The peak parameters are estimated using the estimate_single_peak_stats_psd
function.
Returns
* `peakhists`: Array of histograms for each compton band
* `peakstats`: StructArray of peak parameters for each compton band
* `min_aoe`: Array of minimum A/E values for each compton band
* `max_aoe`: Array of maximum A/E values for each compton band
* `mean_peak_pos`: Mean peak position of all compton bands
* `std_peak_pos`: Standard deviation of the peak position of all compton bands
* `simple_pars_aoe_μ`: Simple curve fit parameters for the peak position energy depencence
* `simple_pars_error_aoe_μ`: Simple curve fit parameter errors for the peak position energy depencence
* `simple_pars_aoe_σ`: Simple curve fit parameters for the peak sigma energy depencence
* `simple_pars_error_aoe_σ`: Simple curve fit parameter errors for the peak sigma energy depencence
LegendSpecFits.get_centered_gaussian_window_cut
— Methodget_centered_gaussian_window_cut(x::Array, min_x::Float64, max_x::Float64, n_σ::Real, center::Float64=0.0, n_bins_cut::Int=500, relative_cut::Float64=0.2, left::Bool=false)
Cut out a single peak from the array x
between min_x
and max_x
by fitting a truncated one-sided Gaussian and extrapolating a window cut with n_σ
standard deviations. The center
and side of the fit can be specified with left
and center
variable.
Returns
* `low_cut`: lower edge of the cut peak
* `high_cut`: upper edge of the cut peak
* `center`: center of the peak
* `σ`: standard deviation of the Gaussian
* `low_cut_fit`: lower edge of the cut peak from the fit
* `high_cut_fit`: upper edge of the cut peak from the fit
* `err`: error of the fit parameters
LegendSpecFits.get_continuum_survival_fraction
— Methodget_continuum_survival_fraction(aoe::Vector{<:Unitful.RealOrRealQuantity}, e::Vector{<:T}, center::T, window::T, aoe_cut::Unitful.RealOrRealQuantity,; inverted_mode::Bool=false, sigma_high_sided::Unitful.RealOrRealQuantity=Inf*unit(first(aoe))) where T<:Unitful.Energy{<:Real}
Get the survival fraction of a continuum after a AoE cut value aoe_cut
for a given center
and window
size.
Returns
center
: Center of the continuumwindow
: Window sizen_before
: Number of counts before the cutn_after
: Number of counts after the cutsf
: Survival fraction
LegendSpecFits.get_distribution_transform
— Functionget_distribution_transform(d::Distribution, pprior::Prior)
Return a DistributionTransform
for the given Distribution
and Prior
.
LegendSpecFits.get_friedman_diaconis_bin_width
— Functionget_friedman_diaconis_bin_width(x::AbstractArray)
Return the bin width for the given data x
using the Friedman-Diaconis rule.
LegendSpecFits.get_low_aoe_cut
— Methodget_low_aoe_cut(aoe::Vector{<:Unitful.RealOrRealQuantity}, e::Vector{<:T},;
dep::T=1592.53u"keV", window::Vector{<:T}=[12.0, 10.0]u"keV", dep_sf::Float64=0.9, rtol::Float64=0.001, maxiters::Int=300, sigma_high_sided::Float64=Inf,
cut_search_interval::Tuple{<:Unitful.RealOrRealQuantity, <:Unitful.RealOrRealQuantity}=(-25.0*unit(first(aoe)), 1.0*unit(first(aoe))),
bin_width_window::T=3.0u"keV", max_e_plot::T=3000.0u"keV", plot_window::Vector{<:T}=[12.0, 50.0]u"keV",
fixed_position::Bool=true, fit_func::Symbol=:gamma_def, uncertainty::Bool=true) where T<:Unitful.Energy{<:Real}
Get the AoE cut value for a given dep
and window
size while performing a peak fit with fixed position. The AoE cut value is determined by finding the cut value for which the number of counts after the cut is equal to dep_sf
times the number of counts before the cut. The algorhithm utilizes a root search algorithm to find the cut value with a relative tolerance of rtol
.
Returns
cut
: AoE cut valuen0
: Number of counts before the cutnsf
: Number of counts after the cut
LegendSpecFits.get_mc_value_shapes
— Methodget_mc_value_shapes(v::NamedTuple, v_err::NamedTuple, n::Integer)
Return a NamedTuple
with the same fields as v
and v_err
but with Normal
distributions for each field.
LegendSpecFits.get_mc_value_shapes
— Methodget_mc_value_shapes(v::NamedTuple, v_err::Matrix, n::Integer)
Generate n
random samples of fit parameters using their respective best-fit values v
and covariance matrix v_err
LegendSpecFits.get_number_of_bins
— Methodget_number_of_bins(x::AbstractArray,; method::Symbol=:sqrt)
Return the number of bins for the given data x
using the given method.
LegendSpecFits.get_peak_fwhm_th228
— Functionget_peak_fwhm_th228(v_ml::NamedTuple, v_ml_err::NamedTuple)
Get the FWHM of a peak from the fit parameters while performing a MC error propagation.
Returns
* `fwhm`: the FWHM of the peak
* `fwhm_err`: the uncertainty of the FWHM of the peak
LegendSpecFits.get_peak_survival_fraction
— Methodget_peak_survival_fraction(aoe::Vector{<:Unitful.RealOrRealQuantity}, e::Vector{<:T}, peak::T, window::Vector{T}, aoe_cut::Unitful.RealOrRealQuantity,;
uncertainty::Bool=true, inverted_mode::Bool=false, bin_width_window::T=2.0u"keV", sigma_high_sided::Unitful.RealOrRealQuantity=Inf*unit(first(aoe)), fit_func::Symbol=:gamma_def) where T<:Unitful.Energy{<:Real}
Get the survival fraction of a peak after a AoE cut value aoe_cut
for a given peak
and window
size while performing a peak fit with fixed position.
Returns
peak
: Peak positionn_before
: Number of counts before the cutn_after
: Number of counts after the cutsf
: Survival fractionerr
: Uncertainties
LegendSpecFits.get_peakhists_th228
— Methodget_peakhists_th228(e::Array, th228_lines::Array, window_sizes::Array, e_unit::String="keV", proxy_binning_peak::Float64=2103.5, proxy_binning_peak_window::Float64=10.0)
Create histograms around the calibration lines and return the histograms and the peak statistics.
Returns
* `peakhists`: array of histograms around the calibration lines
* `peakstats`: array of statistics for the calibration line fits
LegendSpecFits.get_peaks_survival_fractions
— Methodget_peaks_survival_fractions(aoe::Vector{<:Unitful.RealOrRealQuantity}, e::Vector{<:T}, peaks::Vector{<:T}, peak_names::Vector{Symbol}, windows::Vector{<:Tuple{T, T}}, aoe_cut::Unitful.RealOrRealQuantity,; uncertainty::Bool=true, inverted_mode::Bool=false, bin_width_window::T=2.0u"keV", sigma_high_sided::Unitful.RealOrRealQuantity=Inf*unit(first(aoe)), fit_funcs::Vector{Symbol}=fill(:gamma_def, length(peaks))) where T<:Unitful.Energy{<:Real}
Get the survival fraction of a peak after a AoE cut value aoe_cut
for a given peak
and window
size while performing a peak fit with fixed position.
Return
result
: Dict of results for each peakreport
: Dict of reports for each peak
LegendSpecFits.get_residuals
— Methodresiduals(f_fit::Base.Callable, h::Histogram{<:Real,1},v_ml::Union{NamedTuple, AbstractVector})
Calculate bin-wise residuals and normalized residuals. Calcualte bin-wise p-value based on poisson distribution for each bin.
Input:
f_fit
function handle of fit function (peakshape)h
histogram of datav_ml
best-fit parameters
Returns:
residuals
difference: model - data (histogram bin count)residuals_norm
normalized residuals: model - data / sqrt(model)p_value_binwise
p-value for each bin based on poisson distribution
LegendSpecFits.get_sf_after_aoe_cut
— Methodget_sf_after_aoe_cut(aoe_cut::Unitful.RealOrRealQuantity, aoe::Vector{<:Unitful.RealOrRealQuantity}, e::Vector{<:T}, peak::T, window::Vector{T}, bin_width::T, result_before::NamedTuple; uncertainty::Bool=true, fit_func::Symbol=:gamma_def) where T<:Unitful.Energy{<:Real}
Get the survival fraction after a AoE cut value aoe_cut
for a given peak
and window
size from a combined fit to the survived and cut histograms.
Returns
sf
: Survival fraction after the cut
LegendSpecFits.get_th228_fit_functions
— Methodget_th228_fit_functions(; background_center::Union{Real,Nothing} = nothing)
This function defines the gamma peakshape fit functions used in the calibration specfits.
- gamma_def: "default" gamma peakshape with gaussian signal, low-energy tail, and background (flat + step)
- gamma_tails: default gamma peakshape + high-energy tail
- gamma_bckSlope: default gamma peakshape + linear background slope
- gamma_bckExp: default gamma peakshape + exponential background
- gamma_bckFlat: default gamma peakshape - step background (only flat component!)
- gammatailsbckFlat: default gamma peakshape + high-energy tail - step background (only flat component!)
LegendSpecFits.highEtail_peakshape
— MethodhighEtail_peakshape(
x::Real, μ::Real, σ::Real, n::Real,
skew_fraction::Real, skew_width::Real,
)
Describes the high-E signal tail part of the shape
LegendSpecFits.hist_loglike
— Methodhist_loglike(f_fit::Base.Callable, h::Histogram{<:Real,1})
Calculate the Poisson log-likelihood of a fit function f_fit(x)
and a histogram h
. f_fit
must accept all values x
on the horizontal axis of the histogram.
Currently uses a simple midpoint-rule integration of f_fit
over the bins of h
.
LegendSpecFits.linear_function
— Methodlinear_function(x::Real, slope::Real, intercept::Real)
Evaluates a linear function at x
with parameters slope
and intercept
.
LegendSpecFits.lowEtail_peakshape
— MethodlowEtail_peakshape(
x::Real, μ::Real, σ::Real, n::Real,
skew_fraction::Real, skew_width::Real,
)
Describes the low-E signal tail part of the shape of a typical gamma peak in a detector.
LegendSpecFits.lq_drift_time_correction
— Methodlq_norm::Vector{Float64}, dt_eff::Vector{<:Unitful.RealOrRealQuantity}, e_cal::Vector{<:Unitful.Energy{<:Real}}, DEP_µ::Unitful.AbstractQuantity, DEP_σ::Unitful.AbstractQuantity;
DEP_edgesigma::Float64=3.0 , mode::Symbol=:percentile, drift_cutoff_sigma::Float64 = 2.0, prehist_sigma::Float64=2.5, e_expression::Union{String,Symbol}="e", dt_eff_low_quantile::Float64=0.15, dt_eff_high_quantile::Float64=0.95)
Perform the drift time correction on the LQ data using the DEP peak. The function cuts outliers in lq and drift time, then performs a linear fit on the remaining data. The data is Corrected by subtracting the linear fit from the lq data.
Returns
* `result`: NamedTuple of the function used for lq classifier construction
* `report`: NamedTuple of the histograms used for the fit, the cutoff values and the DEP edges
LegendSpecFits.nearestSPD
— MethodnearestSPD(A::Matrix{<:Real})
Returns the nearest positive definite matrix to A Calculation is based on matrix factorization techniques described in https://www.sciencedirect.com/science/article/pii/0024379588902236
LegendSpecFits.p_value
— Methodp_value(f_fit::Base.Callable, h::Histogram{<:Real,1},v_ml::Union{NamedTuple, AbstractVector})
calculate p-value based on least-squares, assuming gaussian uncertainty baseline method to get goodness-of-fit (gof)
input:
f_fit
function handle of fit function (peakshape)h
histogram of datav_ml
best-fit parameters
returns:
pval
p-value of chi2 testchi2
chi2 valuedof
degrees of freedom
LegendSpecFits.p_value_MC
— Methodp_value_MC(f_fit::Base.Callable, h::Histogram{<:Real,1},ps::NamedTuple{(:peak_pos, :peak_fwhm, :peak_sigma, :peak_counts, :mean_background)},v_ml::NamedTuple,;n_samples::Int64=1000)
alternative p-value calculation via Monte Carlo sampling. Warning: computational more expensive than pvaule() and pvalue_LogLikeRatio()
Input:
f_fit
function handle of fit function (peakshape)h
histogram of dataps
best-fit parametersv_ml
best-fit parametersn_samples
number of samples
Performed Steps:
- Create n_samples randomized histograms. For each bin, samples are drawn from a Poisson distribution with λ = model peak shape (best-fit parameter)
- Each sample histogram is fit using the model function
f_fit
- For each sample fit, the max. loglikelihood fit is calculated
Returns
- % p value –> comparison of sample max. loglikelihood and max. loglikelihood of best-fit
LegendSpecFits.p_value_poissonll
— Methodp_value_poissonll(f_fit::Base.Callable, h::Histogram{<:Real,1},v_ml::Union{NamedTuple, AbstractVector})
p-value via poisson likelihood ratio: baseline for ML fits using Poisson statistics and bins with low number of counts
LegendSpecFits.peak_centroid
— Methodpeak_centroid(v::NamedTuple)
calculate centroid of gamma peak from fit parameters
LegendSpecFits.peakshape_components
— Methodpeakshape_components(fit_func::Symbol; background_center::Real)
This function defines the components (signal, low/high-energy tail, backgrounds) of the fit function used in gamma specfits. These component functions are used in the fit-report and in plot receipes
LegendSpecFits.prepare_sep_peakhist
— Methodprepare_sep_peakhist(e::Array{T}, dep::T,; relative_cut::T=0.5, n_bins_cut::Int=500) where T<:Real
Prepare an array of uncalibrated SEP energies for parameter extraction and calibration.
Returns
result
: Result of the initial fitreport
: Report of the initial fit
LegendSpecFits.pulser_cal_qc
— Methodpulser_cal_qc(data, pulser_config; n_pulser_identified=100)
Perform simple QC cuts on the data and return the data for energy calibration.
Returns
- pulser_idx: indices of the pulser events
LegendSpecFits.set_memlimit
— Methodset_memlimit(gig::Float64)
Set memory limit in GB for the whole current process ignoring if things could run in parallel
LegendSpecFits.set_timelimit
— Methodset_timelimit(sec::Float64)
Set time limit in seconds a single Optim.jl optimization step
LegendSpecFits.signal_peakshape
— Methodsignal_peakshape(
x::Real, μ::Real, σ::Real, n::Real,
skew_fraction::Real; skew_fraction_highE::Real = 0.0
)
Describes the signal part of the shape of a typical gamma peak in a detector.
LegendSpecFits.simple_calibration
— Functionsimple_calibration(e_uncal::Array, th228_lines::Array, window_size::Float64=25.0, n_bins::Int=15000, calib_type::String="th228")
Perform a simple calibration for the uncalibrated energy array e_uncal
using the calibration type calib_type
and the calibration lines th228_lines
. The window size is the size of the window around the calibration line to use for the calibration. The number of bins is the number of bins to use for the histogram.
Returns * h_calsimple
: histogram of the calibrated energy array * h_uncal
: histogram of the uncalibrated energy array * c
: calibration factor * fep_guess
: estimated full energy peak (FEP) * peakhists
: array of histograms around the calibration lines * peakstats
: array of statistics for the calibration line fits
LegendSpecFits.sipm_simple_calibration
— Functionsipm_simple_calibration(pe_uncal::Array)
Perform a simple calibration for the uncalibrated p.e. spectrum array pe_uncal
using just the 1 p.e. and 2 p.e. peak positions estimated by a peakfinder.
Inputs: * pe_uncal
: array of uncalibrated peak amplitudes kwargs: * initial_min_amp
: uncalibrated amplitude value as a left boundary to build the uncalibrated histogram where the peak search is performed on. For the peak search with noise peak, this value is consecutively increased i.o.t exclude the noise peak from the histogram. * initial_max_quantile
: quantile of the uncalibrated amplitude array to used as right boundary to build the uncalibrated histogram * peakfinder_σ
: sigma value in number of bins for peakfinder * peakfinder_threshold
: threshold value for peakfinder
Returns * pe_simple_cal
: array of the calibrated pe array with the simple calibration * func
: function to use for the calibration (pe_simple_cal = pe_uncal .* c .+ offset
) * c
: calibration factor * offset
: calibration offset * peakpos
: 1 p.e. and 2 p.e. peak positions in uncalibrated amplitude * peakpos_cal
: 1 p.e. and 2 p.e. peak positions in calibrated amplitude * h_uncal
: histogram of the uncalibrated pe array * h_calsimple
: histogram of the calibrated pe array with the simple calibration
LegendSpecFits.step_gauss
— Methodstep_gauss(x::Real, μ::Real, σ::Real)
Evaluates the convulution of a Heaviside step function and the PDF of Normal(μ, σ)
at x
.
The result does not correspond to a PDF as it is not normalizable.
LegendSpecFits.subhist
— Methodsubhist(h::Histogram, r::Tuple{<:Real,<:Real})
Return a new Histogram
with the bins in the range r
.
LegendSpecFits.tuple_to_array
— Methodtuple_to_array(nt::NamedTuple, fields::Vector{Symbol})
Return an array with the values of the fields in nt
in the order given by fields
.
LegendSpecFits.weibull_from_mx
— Functionweibull_from_mx(m::Real, x::Real, p_x::Real = 0.6827)::Weibull
Construct a Weibull distribution with a given median m
and a given p_x
-quantile x
.
Useful to construct priors for positive quantities.