# pylint: disable=invalid-name
#####################################################################
#This software was developed by the University of Tennessee as part of the
#Distributed Data Analysis of Neutron Scattering Experiments (DANSE)
#project funded by the US National Science Foundation.
#See the license text in license.txt
#copyright 2010, University of Tennessee
######################################################################
"""
This module implements invariant and its related computations.
:author: Gervaise B. Alina/UTK
:author: Mathieu Doucet/UTK
:author: Jae Cho/UTK
:author: Paul Butler/NIST/UD/UTK -- refactor in 2020
"""
from __future__ import division
import math
import numpy as np
from sas.sascalc.dataloader.data_info import Data1D as LoaderData1D
# The minimum q-value to be used when extrapolating
Q_MINIMUM = 1e-5
# The maximum q-value to be used when extrapolating
Q_MAXIMUM = 10
# Number of steps in the extrapolation
INTEGRATION_NSTEPS = 1000
[docs]class Guinier(Transform):
"""
class of type Transform that performs operations related to guinier
function
"""
def __init__(self, scale=1, radius=60):
Transform.__init__(self)
self.scale = scale
self.radius = radius
## Uncertainty of scale parameter
self.dscale = 0
## Unvertainty of radius parameter
self.dradius = 0
[docs] def linearize_q_value(self, value):
"""
Transform the input q-value for linearization
:param value: q-value
:return: q*q
"""
return value * value
[docs] def evaluate_model(self, x):
"""
return F(x)= scale* e-((radius*x)**2/3)
"""
return self._guinier(x)
[docs] def evaluate_model_errors(self, x):
"""
Returns the error on I(q) for the given array of q-values
:param x: array of q-values
"""
p1 = np.array([self.dscale * math.exp(-((self.radius * q) ** 2 / 3)) \
for q in x])
p2 = np.array([self.scale * math.exp(-((self.radius * q) ** 2 / 3))\
* (-(q ** 2 / 3)) * 2 * self.radius * self.dradius for q in x])
diq2 = p1 * p1 + p2 * p2
return np.array([math.sqrt(err) for err in diq2])
def _guinier(self, x):
"""
Retrieve the guinier function after apply an inverse guinier function
to x
Compute a F(x) = scale* e-((radius*x)**2/3).
:param x: a vector of q values
:param scale: the scale value
:param radius: the guinier radius value
:return: F(x)
"""
# transform the radius of coming from the inverse guinier function to a
# a radius of a guinier function
if self.radius <= 0:
msg = "Rg expected positive value, but got %s" % self.radius
raise ValueError(msg)
value = np.array([math.exp(-((self.radius * i) ** 2 / 3)) for i in x])
return self.scale * value
[docs]class PowerLaw(Transform):
"""
class of type transform that perform operation related to power_law
function
"""
def __init__(self, scale=1, power=4):
Transform.__init__(self)
self.scale = scale
self.power = power
self.dscale = 0.0
self.dpower = 0.0
[docs] def linearize_q_value(self, value):
"""
Transform the input q-value for linearization
:param value: q-value
:return: log(q)
"""
return math.log(value)
[docs] def evaluate_model(self, x):
"""
given a scale and a radius transform x, y using a power_law
function
"""
return self._power_law(x)
[docs] def evaluate_model_errors(self, x):
"""
Returns the error on I(q) for the given array of q-values
:param x: array of q-values
"""
p1 = np.array([self.dscale * math.pow(q, -self.power) for q in x])
p2 = np.array([self.scale * self.power * math.pow(q, -self.power - 1)\
* self.dpower for q in x])
diq2 = p1 * p1 + p2 * p2
return np.array([math.sqrt(err) for err in diq2])
def _power_law(self, x):
"""
F(x) = scale* (x)^(-power)
when power= 4. the model is porod
else power_law
The model has three parameters: ::
1. x: a vector of q values
2. power: power of the function
3. scale : scale factor value
:param x: array
:return: F(x)
"""
if self.power <= 0:
msg = "Power_law function expected positive power,"
msg += " but got %s" % self.power
raise ValueError(msg)
if self.scale <= 0:
msg = "scale expected positive value, but got %s" % self.scale
raise ValueError(msg)
value = np.array([math.pow(i, -self.power) for i in x])
return self.scale * value
[docs]class InvariantCalculator(object):
"""
Compute invariant if data is given.
Can provide volume fraction and surface area if the user provides
Porod constant and contrast values.
:precondition: the user must send a data of type DataLoader.Data1D
the user provide background and scale values.
:note: Some computations depends on each others.
"""
def __init__(self, data, background=0, scale=1):
"""
Initialize variables.
:param data: data must be of type DataLoader.Data1D
:param background: Background value. The data will be corrected
before processing
:param scale: Scaling factor for I(q). The data will be corrected
before processing
"""
# Background and scale should be private data member if the only way to
# change them are by instantiating a new object.
self._background = background
self._scale = scale
# slit height for smeared data
self._smeared = None
# The data should be private
self._data = self._get_data(data)
# get the dxl if the data is smeared: This is done only once on init.
if self._data.dxl is not None and self._data.dxl.all() > 0:
# assumes constant dxl
self._smeared = self._data.dxl[0]
# Since there are multiple variants of Q*, you should force the
# user to use the get method and keep Q* a private data member
self._qstar = None
# You should keep the error on Q* so you can reuse it without
# recomputing the whole thing.
self._qstar_err = 0
# Extrapolation parameters
self._low_extrapolation_npts = 4
self._low_extrapolation_function = Guinier()
self._low_extrapolation_power = None
self._low_extrapolation_power_fitted = None
self._high_extrapolation_npts = 4
self._high_extrapolation_function = PowerLaw()
self._high_extrapolation_power = None
self._high_extrapolation_power_fitted = None
# Extrapolation range
self._low_q_limit = Q_MINIMUM
def _get_data(self, data):
"""
:note: this function must be call before computing any type
of invariant
:return: new data = self._scale *data - self._background
"""
if not issubclass(data.__class__, LoaderData1D):
#Process only data that inherited from DataLoader.Data_info.Data1D
raise ValueError("Data must be of type DataLoader.Data1D")
#from copy import deepcopy
new_data = (self._scale * data) - self._background
# Check that the vector lengths are equal
assert len(new_data.x) == len(new_data.y)
# Verify that the errors are set correctly
if new_data.dy is None or len(new_data.x) != len(new_data.dy) or \
(min(new_data.dy) == 0 and max(new_data.dy) == 0):
new_data.dy = np.ones(len(new_data.x))
return new_data
def _fit(self, model, qmin=Q_MINIMUM, qmax=Q_MAXIMUM, power=None):
"""
fit data with function using
data = self._get_data()
fx = Functor(data , function)
y = data.y
slope, constant = linalg.lstsq(y,fx)
:param qmin: data first q value to consider during the fit
:param qmax: data last q value to consider during the fit
:param power : power value to consider for power-law
:param function: the function to use during the fit
:return a: the scale of the function
:return b: the other parameter of the function for guinier will be radius
for power_law will be the power value
"""
extrapolator = Extrapolator(data=self._data, model=model)
p, dp = extrapolator.fit(power=power, qmin=qmin, qmax=qmax)
return model.extract_model_parameters(constant=p[1], slope=p[0],
dconstant=dp[1], dslope=dp[0])
def _get_qstar(self, data):
"""
Compute invariant for pinhole data.
This invariant is given by: ::
q_star = x0**2 *y0 *dx0 +x1**2 *y1 *dx1
+ ..+ xn**2 *yn *dxn for non smeared data
q_star = dxl0 *x0 *y0 *dx0 +dxl1 *x1 *y1 *dx1
+ ..+ dlxn *xn *yn *dxn for smeared data
where n >= len(data.x)-1
dxl = slit height dQl
dxi = 1/2*(xi+1 - xi) + (xi - xi-1)
dx0 = (x1 - x0)/2
dxn = (xn - xn-1)/2
:param data: the data to use to compute invariant.
:return q_star: invariant value for pinhole data. q_star > 0
"""
if len(data.x) <= 1 or len(data.y) <= 1 or len(data.x) != len(data.y):
msg = "Length x and y must be equal"
msg += " and greater than 1; got x=%s, y=%s" % (len(data.x), len(data.y))
raise ValueError(msg)
else:
# Take care of smeared data
if self._smeared is None:
gx = data.x * data.x
# assumes that len(x) == len(dxl).
else:
gx = data.dxl * data.x
n = len(data.x) - 1
#compute the first delta q
dx0 = (data.x[1] - data.x[0]) / 2
#compute the last delta q
dxn = (data.x[n] - data.x[n - 1]) / 2
total = 0
total += gx[0] * data.y[0] * dx0
total += gx[n] * data.y[n] * dxn
if len(data.x) == 2:
return total
else:
#iterate between for element different
#from the first and the last
for i in range(1, n - 1):
dxi = (data.x[i + 1] - data.x[i - 1]) / 2
total += gx[i] * data.y[i] * dxi
return total
def _get_qstar_uncertainty(self, data):
"""
Compute invariant uncertainty with with pinhole data.
This uncertainty is given as follow: ::
dq_star = math.sqrt[(x0**2*(dy0)*dx0)**2 +
(x1**2 *(dy1)*dx1)**2 + ..+ (xn**2 *(dyn)*dxn)**2 ]
where n >= len(data.x)-1
dxi = 1/2*(xi+1 - xi) + (xi - xi-1)
dx0 = (x1 - x0)/2
dxn = (xn - xn-1)/2
dyn: error on dy
:param data:
:note: if data doesn't contain dy return "None"
"""
if len(data.x) <= 1 or len(data.y) <= 1 or \
len(data.x) != len(data.y) or \
(data.dy is not None and (len(data.dy) != len(data.y))):
msg = "Length of data.x and data.y must be equal"
msg += " and greater than 1; got x=%s, y=%s" % (len(data.x), len(data.y))
raise ValueError(msg)
else:
# For reduced data sqrt(I) is incorrect! if the data has no dy
# then we should not invent it and then propogate that completely
# bogus value. So changed behaviour on Mar 23, 2020 to return
# None instead
if data.dy is None:
return None
dy = data.dy
# Take care of smeared data
if self._smeared is None:
gx = data.x * data.x
# assumes that len(x) == len(dxl).
else:
gx = data.dxl * data.x
n = len(data.x) - 1
#compute the first delta
dx0 = (data.x[1] - data.x[0]) / 2
#compute the last delta
dxn = (data.x[n] - data.x[n - 1]) / 2
total = 0
total += (gx[0] * dy[0] * dx0) ** 2
total += (gx[n] * dy[n] * dxn) ** 2
if len(data.x) == 2:
return math.sqrt(total)
else:
#iterate between for element different
#from the first and the last
for i in range(1, n - 1):
dxi = (data.x[i + 1] - data.x[i - 1]) / 2
total += (gx[i] * dy[i] * dxi) ** 2
return math.sqrt(total)
def _get_extrapolated_data(self, model, npts=INTEGRATION_NSTEPS,
q_start=Q_MINIMUM, q_end=Q_MAXIMUM):
"""
:return: extrapolate data create from data
"""
#create new Data1D to compute the invariant
q = np.linspace(start=q_start,
stop=q_end,
num=npts,
endpoint=True)
iq = model.evaluate_model(q)
diq = model.evaluate_model_errors(q)
result_data = LoaderData1D(x=q, y=iq, dy=diq)
if self._smeared is not None:
result_data.dxl = self._smeared * np.ones(len(q))
return result_data
[docs] def get_data(self):
"""
:return: self._data
"""
return self._data
[docs] def get_qstar_low(self):
"""
Compute the invariant for extrapolated data at low q range.
Implementation:
data = self._get_extra_data_low()
return self._get_qstar()
:return q_star: the invariant for data extrapolated at low q.
"""
# Data boundaries for fitting
qmin = self._data.x[0]
qmax = self._data.x[int(self._low_extrapolation_npts - 1)]
# Extrapolate the low-Q data
p, _ = self._fit(model=self._low_extrapolation_function,
qmin=qmin,
qmax=qmax,
power=self._low_extrapolation_power)
self._low_extrapolation_power_fitted = p[0]
# Distribution starting point
self._low_q_limit = Q_MINIMUM
if Q_MINIMUM >= qmin:
self._low_q_limit = qmin / 10
data = self._get_extrapolated_data(\
model=self._low_extrapolation_function,
npts=INTEGRATION_NSTEPS,
q_start=self._low_q_limit, q_end=qmin)
# Systematic error
# If we have smearing, the shape of the I(q) distribution at low Q will
# may not be a Guinier or simple power law. The following is
# a conservative estimation for the systematic error.
err = qmin * qmin * math.fabs((qmin - self._low_q_limit) * \
(data.y[0] - data.y[INTEGRATION_NSTEPS - 1]))
return self._get_qstar(data), self._get_qstar_uncertainty(data) + err
[docs] def get_qstar_high(self):
"""
Compute the invariant for extrapolated data at high q range.
Implementation:
data = self._get_extra_data_high()
return self._get_qstar()
:return q_star: the invariant for data extrapolated at high q.
"""
# Data boundaries for fitting
x_len = len(self._data.x) - 1
qmin = self._data.x[int(x_len - (self._high_extrapolation_npts - 1))]
qmax = self._data.x[int(x_len)]
# fit the data with a model to get the appropriate parameters
p, _ = self._fit(model=self._high_extrapolation_function,
qmin=qmin,
qmax=qmax,
power=self._high_extrapolation_power)
self._high_extrapolation_power_fitted = p[0]
#create new Data1D to compute the invariant
data = self._get_extrapolated_data(\
model=self._high_extrapolation_function,
npts=INTEGRATION_NSTEPS,
q_start=qmax, q_end=Q_MAXIMUM)
return self._get_qstar(data), self._get_qstar_uncertainty(data)
[docs] def get_qstar(self, extrapolation=None):
"""
Compute the invariant of the local copy of data.
:param extrapolation: string to apply optional extrapolation
:return q_star: invariant of the data within data's q range
:warning: When using setting data to Data1D ,
the user is responsible of
checking that the scale and the background are
properly apply to the data
"""
self._qstar = self._get_qstar(self._data)
self._qstar_err = self._get_qstar_uncertainty(self._data)
if extrapolation is None:
return self._qstar
# Compute invariant plus invariant of extrapolated data
extrapolation = extrapolation.lower()
if extrapolation == "low":
qs_low, dqs_low = self.get_qstar_low()
qs_hi, dqs_hi = 0, 0
elif extrapolation == "high":
qs_low, dqs_low = 0, 0
qs_hi, dqs_hi = self.get_qstar_high()
elif extrapolation == "both":
qs_low, dqs_low = self.get_qstar_low()
qs_hi, dqs_hi = self.get_qstar_high()
self._qstar += qs_low + qs_hi
self._qstar_err = math.sqrt(self._qstar_err * self._qstar_err \
+ dqs_low * dqs_low + dqs_hi * dqs_hi)
return self._qstar
[docs] def get_surface(self, contrast, porod_const, extrapolation=None):
"""
Compute the specific surface from the data.
Historically, Sv was computed with the invariant and the Porod
constant so as not to have to know the contrast in order to get the
Sv as:
surface = (pi * V * (1- V) * porod_const) / q_star
However, that turns out to be a pointless exercise since it
also requires a knowledge of the volume fractions and from the
volumer fraction and the invariant the contrast can be calculated as:
contrast**2 = q_star / (2 * pi**2 * V * (1- V))
Thus either way, mathematically it is always identical to computing
with only the contrast and the Porod Constant. up to and including
SasView versions 4.2.2 and 5.0.1 the implementation used the traditional
circular approach.
Implementation: ::
Given the above, as of SasView 4.3 and 5.0.2 we compute Sv simply
from the Porod Constant and the contrast between the two phases as:
surface = porod_const / (2 * pi contrast**2)
:param contrast: contrast between the two phases
:param porod_const: Porod constant
:param extrapolation: string to apply optional extrapolation. This will
only be needed if and when the contrast term is calculated from
the invariant.
:return: specific surface
"""
# convert porod_const to units of A^-5 instead of cm^-1 A^-4 so that
# s is returned in units of 1/A.
_porod_const = 1.0e-8 * porod_const
return _porod_const / (2 * math.pi * math.fabs(contrast)**2)
[docs] def get_volume_fraction(self, contrast, extrapolation=None):
"""
Compute volume fraction is deduced as follow: ::
q_star = 2*(pi*contrast)**2* volume( 1- volume)
for k = 10^(-8)*q_star/(2*(pi*|contrast|)**2)
we get 2 values of volume:
with 1 - 4 * k >= 0
volume1 = (1- sqrt(1- 4*k))/2
volume2 = (1+ sqrt(1- 4*k))/2
q_star: the invariant value included extrapolation is applied
unit 1/A^(3)*1/cm
q_star = self.get_qstar()
the result returned will be 0 <= volume <= 1
:param contrast: contrast value provides by the user of type float.
contrast unit is 1/A^(2)= 10^(16)cm^(2)
:param extrapolation: string to apply optional extrapolation
:return: volume fraction
:note: volume fraction must have no unit
"""
if contrast <= 0:
raise ValueError("The contrast parameter must be greater than zero")
# Make sure Q star is up to date
self.get_qstar(extrapolation)
if self._qstar <= 0:
msg = "Invalid invariant: Invariant Q* must be greater than zero"
raise RuntimeError(msg)
# Compute intermediate constant
k = 1.e-8 * self._qstar / (2 * (math.pi * math.fabs(float(contrast))) ** 2)
# Check discriminant value
discrim = 1 - 4 * k
# Compute volume fraction
if discrim < 0:
msg = "Could not compute the volume fraction: negative discriminant"
raise RuntimeError(msg)
elif discrim == 0:
return 1 / 2
else:
volume1 = 0.5 * (1 - math.sqrt(discrim))
volume2 = 0.5 * (1 + math.sqrt(discrim))
if 0 <= volume1 and volume1 <= 1:
return volume1
elif 0 <= volume2 and volume2 <= 1:
return volume2
msg = "Could not compute the volume fraction: inconsistent results"
raise RuntimeError(msg)
[docs] def get_qstar_with_error(self, extrapolation=None):
"""
Compute the invariant uncertainty.
This uncertainty computation depends on whether or not the data is
smeared.
:param extrapolation: string to apply optional extrapolation
:return: invariant, the invariant uncertainty
"""
self.get_qstar(extrapolation)
return self._qstar, self._qstar_err
[docs] def get_volume_fraction_with_error(self, contrast, extrapolation=None):
"""
Compute uncertainty on volume value as well as the volume fraction
This uncertainty is given by the following equation: ::
sigV = dV/dq_star * sigq_star
so that
sigV = (k * sigq_star) /(q_star * math.sqrt(1 - 4 * k))
for k = 10^(-8)*q_star/(2*(pi*|contrast|)**2)
10^(-8) converts from cm^-1 to A^-1
q_star: the invariant, in cm^-1A^-3, including extrapolated values
if they have been requested
dq_star: the invariant uncertainty
dV: the volume uncertainty
The uncertainty will be set to -1 if it can't be computed.
:param contrast: contrast value
:param extrapolation: string to apply optional extrapolation
:return: V, dV = volume fraction, error on volume fraction
"""
volume = self.get_volume_fraction(contrast, extrapolation)
# Compute error
k = 1.e-8 * self._qstar / (2 * (math.pi * \
math.fabs(float(contrast)))** 2)
# Check value inside the sqrt function
value = 1 - k * self._qstar
if (value) <= 0:
uncertainty = -1
else:
# Compute uncertainty
uncertainty = math.fabs((k * self._qstar_err)
/ (self._qstar * math.sqrt(1 - 4 * k)))
return volume, uncertainty
[docs] def get_surface_with_error(self, contrast, porod_const, extrapolation=None):
"""
As of SasView 4.3 and 5.0.3, the specific surface is computed directly
from the contrast and porod_constant wich are currently user inputs
with no option for any uncertainty so no uncertainty can be calculated.
However we include the uncertainty computation for future use if and
when these values get an uncertainty. This is given as:
ds = sqrt[(s'_cp)**2 * dcp**2 + (s'_contrast)**2 * dcontrast**2]
where s'_x is the partial derivative of S with respect to x
which gives (this should be checked before using in anger)
ds = sqrt((dporod_const**2 * contrast**2 + 4 * (porod_const *
dcontrast)**2) / (4 * pi**2 * contrast**6))
We also assume some users will never enter a value for uncertainty so
allow for None even when it is an option.
:param contrast: contrast value eventually with the error
:param porod_const: porod constant value eventually with the error
:param extrapolation: string to apply optional extrapolation. This will
only be needed if and when the contrast term is calculated from
the invariant.
:return s, ds: the surface, with its uncertainty
"""
# until contrast and porod_constant are given with uncertainties set
# them to 0
dcontrast = None
dporod_const = None
# IMPORTATN: the porod constant (and eventually its uncertainty) are
# given in units of cm^-1 A^-4. We need to be mindfult of units when
# writing equations. Thus for computing ds both the porod constant and
# its uncertainty need to be converted to A^-5 so they play well with
# the contrast which is in A-2.
# Note that the porod constant is converted in self.get_surface method
#so do NOT convert before calling here
s = self.get_surface(contrast=contrast, porod_const=porod_const)
# Until uncertainties in contrast and the Porod Constant are provided
# just return nothing.
ds = None
# When they are available, use the following:
# if dporod_const is None:
# _dporod_const = 0.
# else:
# _dporod_const = dporod_const * 1e-8
# if dcontrast is None:
# dcontrast = 0.
# For this new computation we DO need to convert the units
# _porod_const = porod_const * 1e-8
#ds = math.sqrt((_dporod_const**2 * contrast**2 + 4 * (_porod_const *
# dcontrast)**2 / (4 * math.pi**2 * constrast**6))
return s, ds