slope.m

基于matlab的反演程序,用于地球物理勘探中射线追踪及偏移成像程序.

function s=slope(x,y,xnot)

% s=slope(x,y,xnot)
%
% compute the slope of the curve given by x,y at the point xnot. If the curve
% is multivalued, then multiple s's will be returned. If the curve is a polygon, then
% it must have its first and last points explicitly equal. The curve is assumed 
% piecewise linear. If xnot is exactly equal to a point in x, then the slope 
% returned is the average of the segments before and after xnot.
%
% NOTE: It is illegal for you to use this software for a purpose other
% than non-profit education or research UNLESS you are employed by a CREWES
% Project sponsor. By using this software, you are agreeing to the terms
% detailed in this software's Matlab source file.
 
% BEGIN TERMS OF USE LICENSE
%
% This SOFTWARE is maintained by the CREWES Project at the Department
% of Geology and Geophysics of the University of Calgary, Calgary,
% Alberta, Canada.  The copyright and ownership is jointly held by 
% its author (identified above) and the CREWES Project.  The CREWES 
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	ind=find(x==xnot);
	if(isempty(ind))
		ind=surround(x,xnot);
		s=(y(ind)-y(ind+1))./(x(ind)-x(ind+1));
	else
			n=length(x);
			% extrapolate ends for end conditions
			m1=(y(2)-y(1))/(x(2)-x(1));
			x0=x(1)-(x(2)-x(1));
			y0=y(1)+(x0-x(1))*m1;
			mn=(y(n)-y(n-1))/(x(n)-x(n-1));
			xn1=x(n)+(x(n)-x(n-1));
			yn1=y(n)+(xn1-x(n))*mn;
			x=[x0 x xn1];% pad first and last samples for end conditions
			y=[y0 y yn1];
			ind=ind+1;
			s1=(y(ind)-y(ind+1))./(x(ind)-x(ind+1));
			s2=(y(ind-1)-y(ind))./(x(ind-1)-x(ind));
		s=.5*(s1+s2);
	end