# source:sasview/src/sas/sasgui/perspectives/pr/media/pr_help.rst@1f1e4f0

ESS_GUIESS_GUI_DocsESS_GUI_batch_fittingESS_GUI_bumps_abstractionESS_GUI_iss1116ESS_GUI_iss879ESS_GUI_iss959ESS_GUI_openclESS_GUI_orderingESS_GUI_sync_sascalc
Last change on this file since 1f1e4f0 was 1f1e4f0, checked in by Piotr Rozyczko <rozyczko@…>, 8 years ago

Word 'perspective' removed as per #513

• Property mode set to `100644`
File size: 1.8 KB
RevLine
[ec392464]1.. pr_help.rst
2
3.. This is a port of the original SasView html help file to ReSTructured text
4.. by S King, ISIS, during SasView CodeCamp-III in Feb 2015.
5
[1f1e4f0]6P(r) Calculation
7================
[ec392464]8
[8a22b5b]9Description
10-----------
[ec392464]11
[8a22b5b]12This tool calculates a real-space distance distribution function, *P(r)*, using
13the inversion approach (Moore, 1908).
14
15*P(r)* is set to be equal to an expansion of base functions of the type
16
17  |bigphi|\_n(r) = 2.r.sin(|pi|\ .n.r/D_max)
[ec392464]18
19The coefficient of each base function in the expansion is found by performing
[8a22b5b]20a least square fit with the following fit function
21
22  |chi|\ :sup:`2` = |bigsigma|\ :sub:`i` [ I\ :sub:`meas`\ (Q\ :sub:`i`\ ) - I\ :sub:`th`\ (Q\ :sub:`i`\ ) ] :sup:`2` / (Error) :sup:`2` + Reg_term
[ec392464]23
[8a22b5b]24where I\ :sub:`meas`\ (Q) is the measured scattering intensity and
25I\ :sub:`th`\ (Q) is the prediction from the Fourier transform of the *P(r)*
26expansion.
[ec392464]27
[8a22b5b]28The *Reg_term* term is a regularization term set to the second derivative
29d\ :sup:`2`\ *P(r)* / dr\ :sup:`2` integrated over *r*. It is used to produce a
30smooth *P(r)* output.
[ec392464]31
[8a22b5b]32.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
[ec392464]33
[1f1e4f0]34Using P(r) inversion
35--------------------
[ec392464]36
[8a22b5b]37The user must enter
38
39*  *Number of terms*: the number of base functions in the P(r) expansion.
[ec392464]40
[8a22b5b]41*  *Regularization constant*: a multiplicative constant to set the size of
[ec392464]42   the regularization term.
43
[8a22b5b]44*  *Maximum distance*: the maximum distance between any two points in the
[ec392464]45   system.
[8a22b5b]46
47.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
48
49Reference
50---------
51
52P.B. Moore
53*J. Appl. Cryst.*, 13 (1980) 168-175
54
55.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
56
[a9dc4eb]57.. note::  This help document was last changed by Steve King, 01May2015
Note: See TracBrowser for help on using the repository browser.