/usr/lib/python3/dist-packages/sasmodels/sesans.py is in python3-sasmodels 0.97~git20171104-2.
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Conversion of scattering cross section from SANS (I(q), or rather, ds/dO) in absolute
units (cm-1)into SESANS correlation function G using a Hankel transformation, then converting
the SESANS correlation function into polarisation from the SESANS experiment
Everything is in units of metres except specified otherwise (NOT TRUE!!!)
Everything is in conventional units (nm for spin echo length)
Wim Bouwman (w.g.bouwman@tudelft.nl), June 2013
"""
from __future__ import division
import numpy as np # type: ignore
from numpy import pi, exp # type: ignore
from scipy.special import j0
class SesansTransform(object):
"""
Spin-Echo SANS transform calculator. Similar to a resolution function,
the SesansTransform object takes I(q) for the set of *q_calc* values and
produces a transformed dataset
*SElength* (A) is the set of spin-echo lengths in the measured data.
*zaccept* (1/A) is the maximum acceptance of scattering vector in the spin
echo encoding dimension (for ToF: Q of min(R) and max(lam)).
*Rmax* (A) is the maximum size sensitivity; larger radius requires more
computation time.
"""
#: SElength from the data in the original data units; not used by transform
#: but the GUI uses it, so make sure that it is present.
q = None # type: np.ndarray
#: q values to calculate when computing transform
q_calc = None # type: np.ndarray
# transform arrays
_H = None # type: np.ndarray
_H0 = None # type: np.ndarray
def __init__(self, z, SElength, lam, zaccept, Rmax):
# type: (np.ndarray, float, float) -> None
#import logging; logging.info("creating SESANS transform")
self.q = z
self._set_hankel(SElength, lam, zaccept, Rmax)
def apply(self, Iq):
# tye: (np.ndarray) -> np.ndarray
G0 = np.dot(self._H0, Iq)
G = np.dot(self._H.T, Iq)
P = G - G0
return P
def _set_hankel(self, SElength, lam, zaccept, Rmax):
# type: (np.ndarray, float, float) -> None
# Force float32 arrays, otherwise run into memory problems on some machines
SElength = np.asarray(SElength, dtype='float32')
#Rmax = #value in text box somewhere in FitPage?
q_max = 2*pi / (SElength[1] - SElength[0])
q_min = 0.1 * 2*pi / (np.size(SElength) * SElength[-1])
q = np.arange(q_min, q_max, q_min, dtype='float32')
dq = q_min
H0 = np.float32(dq/(2*pi)) * q
repq = np.tile(q, (SElength.size, 1)).T
repSE = np.tile(SElength, (q.size, 1))
H = np.float32(dq/(2*pi)) * j0(repSE*repq) * repq
replam = np.tile(lam, (q.size, 1))
reptheta = np.arcsin(repq*replam/2*np.pi)
mask = reptheta > zaccept
H[mask] = 0
self.q_calc = q
self._H, self._H0 = H, H0
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