%       Copyright (c) 2000 Bruce Ravel
%       Permission is granted to copy, distribute and/or modify this
%       document under the terms of the GNU Free Documentation License,
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%       Foundation; with the Invariant Sections being "EXAFS Analysis
%       Using FEFF and FEFFIT, Part 1: Presentation", "EXAFS Analysis
%       Using FEFF and FEFFIT, Part 2: Commentary", and all related
%       analysis examples, with no Front-Cover Texts, and with no
%       Back-Cover Texts.  A copy of the license is included in the
%       section entitled "GNU Free Documentation License".
% 
% 
% This file (and all files associated with `EXAFS Analysis Using FEFF
% and FEFFIT') are free documentation; you can redistribute it and/or
% modify it under the terms of the GNU Free Documentation License as
% published by the Free Software Foundation; either version 1, or (at
% your option) any later version.
% 
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% along with `EXAFS Analysis Using FEFF and FEFFIT'; see the file
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%% This file defines constraints between the fitting parameters and
%% the crystal parameters.  It calculates such things as inter-atomic
%% bond lengths and interpolation coefficients for measuring the
%% Ti-Opl-Ti scattering angle.

%%% crystalography model:

%%% length of a axis
set	a		a0 + del_a

%%% length of c axis
% set	c		c0 + del_c

set	vol		a0*a0*c0
set	c		vol / (a^2)

%%% short and long axial oxygen bond lengths
set	rtio1_sh	(0.5 - (doax-dti)) * c
set	rtio1_lo	(0.5 + (doax-dti)) * c

%%% planar oxygen bond length
set	rtio2		sqrt( (a/2)^2 + ((dopl-dti)*c)^2 )

%%% short and long lead bond length
set	rtipb_sh	sqrt( a^2/2 + c^2*(0.5 - dti)^2 )
set	rtipb_lo	sqrt( a^2/2 + c^2*(0.5 + dti)^2 )

%%% buckling angle & weighting coefficients
%%% see Num. Rec. in Fort. 1992 ed, sec. 3.1, p. 102, Lagrange's formula
set	angle		acos( a/(2*rtio2) ) * (180/pi)
set	delth		0
set	x		(angle / angle0)^2 
% set	x		( angle^2 + delth^2 ) / angle0^2 

%% Two point interpolation
set	w_full		x
set	w_twoth		0
set	w_zero		1-x

%% Three point interpolation
% set	w_full		3*x^2 - 2*x
% set	w_twoth		(-9/2) * x * (x-1)
% set	w_zero		1.5 * (x-1) * (x-2/3)

set	sigang		epsilon * delth * angle



!!&& Local Variables:
!!&& input-out-path: "fits/"
!!&& input-feff-path: "feff/"
!!&& input-data-path: "data/"
!!&& input-program-name: "feffit"
!!&& End:
%# Input-mode Time-stamp: <2000/03/11 21:11:34 bruce>