[c97724e] | 1 | """ |
---|
[d459d4e] | 2 | Conversion of scattering cross section from SANS (I(q), or rather, ds/dO) in absolute |
---|
| 3 | units (cm-1)into SESANS correlation function G using a Hankel transformation, then converting |
---|
| 4 | the SESANS correlation function into polarisation from the SESANS experiment |
---|
[c97724e] | 5 | |
---|
[d459d4e] | 6 | Everything is in units of metres except specified otherwise (NOT TRUE!!!) |
---|
| 7 | Everything is in conventional units (nm for spin echo length) |
---|
[c97724e] | 8 | |
---|
| 9 | Wim Bouwman (w.g.bouwman@tudelft.nl), June 2013 |
---|
| 10 | """ |
---|
| 11 | |
---|
| 12 | from __future__ import division |
---|
| 13 | |
---|
[7ae2b7f] | 14 | import numpy as np # type: ignore |
---|
| 15 | from numpy import pi, exp # type: ignore |
---|
[54f1d96] | 16 | from scipy.special import j0 |
---|
[94d13f1] | 17 | |
---|
[54f1d96] | 18 | class SesansTransform(object): |
---|
[94d13f1] | 19 | """ |
---|
| 20 | Spin-Echo SANS transform calculator. Similar to a resolution function, |
---|
| 21 | the SesansTransform object takes I(q) for the set of *q_calc* values and |
---|
| 22 | produces a transformed dataset |
---|
| 23 | |
---|
| 24 | *SElength* (A) is the set of spin-echo lengths in the measured data. |
---|
| 25 | |
---|
| 26 | *zaccept* (1/A) is the maximum acceptance of scattering vector in the spin |
---|
| 27 | echo encoding dimension (for ToF: Q of min(R) and max(lam)). |
---|
| 28 | |
---|
| 29 | *Rmax* (A) is the maximum size sensitivity; larger radius requires more |
---|
| 30 | computation time. |
---|
| 31 | """ |
---|
| 32 | #: SElength from the data in the original data units; not used by transform |
---|
| 33 | #: but the GUI uses it, so make sure that it is present. |
---|
[54f1d96] | 34 | q = None # type: np.ndarray |
---|
| 35 | |
---|
[94d13f1] | 36 | #: q values to calculate when computing transform |
---|
| 37 | q_calc = None # type: np.ndarray |
---|
| 38 | |
---|
[54f1d96] | 39 | # transform arrays |
---|
[94d13f1] | 40 | _H = None # type: np.ndarray |
---|
| 41 | _H0 = None # type: np.ndarray |
---|
[54f1d96] | 42 | |
---|
[94d13f1] | 43 | def __init__(self, z, SElength, zaccept, Rmax): |
---|
| 44 | # type: (np.ndarray, float, float) -> None |
---|
| 45 | #import logging; logging.info("creating SESANS transform") |
---|
| 46 | self.q = z |
---|
| 47 | self._set_hankel(SElength, zaccept, Rmax) |
---|
[54f1d96] | 48 | |
---|
| 49 | def apply(self, Iq): |
---|
[94d13f1] | 50 | # tye: (np.ndarray) -> np.ndarray |
---|
| 51 | G0 = np.dot(self._H0, Iq) |
---|
| 52 | G = np.dot(self._H.T, Iq) |
---|
[54f1d96] | 53 | P = G - G0 |
---|
| 54 | return P |
---|
| 55 | |
---|
[94d13f1] | 56 | def _set_hankel(self, SElength, zaccept, Rmax): |
---|
| 57 | # type: (np.ndarray, float, float) -> None |
---|
| 58 | # Force float32 arrays, otherwise run into memory problems on some machines |
---|
| 59 | SElength = np.asarray(SElength, dtype='float32') |
---|
[54f1d96] | 60 | |
---|
[94d13f1] | 61 | #Rmax = #value in text box somewhere in FitPage? |
---|
| 62 | q_max = 2*pi / (SElength[1] - SElength[0]) |
---|
| 63 | q_min = 0.1 * 2*pi / (np.size(SElength) * SElength[-1]) |
---|
| 64 | q = np.arange(q_min, q_max, q_min, dtype='float32') |
---|
| 65 | dq = q_min |
---|
[54f1d96] | 66 | |
---|
[94d13f1] | 67 | H0 = np.float32(dq/(2*pi)) * q |
---|
[54f1d96] | 68 | |
---|
[94d13f1] | 69 | repq = np.tile(q, (SElength.size, 1)).T |
---|
| 70 | repSE = np.tile(SElength, (q.size, 1)) |
---|
| 71 | H = np.float32(dq/(2*pi)) * j0(repSE*repq) * repq |
---|
| 72 | |
---|
| 73 | self.q_calc = q |
---|
| 74 | self._H, self._H0 = H, H0 |
---|