interpnan.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 y0=internan(x,y,x0)

% y0=interpnan(x,y,x0)
%
% INTERP is similar to MATLAB's INTERP1 unless x contains nans.
% If nans are present, then they are assumed to mark distinct segments
% of x which are handled independently. Each such segment must obey the
% usual restrictions imposed by interp1 (i.e. monotonic) but there need
% be no relation between the segments.
% If x contains no nans, there is still a difference between this and
% interp1. The latter will bomb if any x0 lie outside the range of x.
% This routine will not bomb and returns nans instead. Note that the
% actual interpolator used is lint not interp1 because lint is more 
% efficient when length(x0) >> length(x) .
%
% G.F. Margrave Jan 1995
%
% 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
%
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% of Geology and Geophysics of the University of Calgary, Calgary,
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y0=nan*ones(size(x0));

%test for segments
ind=find(isnan(x));
ind=[0 ind length(x)+1];

nsegs=length(ind)-1;

for k=1:nsegs
	%determine indicies for the segment
	iseg=ind(k)+1:ind(k+1)-1;
	if(length(iseg))% severl nans in a row produce zero length segments
		%now determine which x0 sites lie within the current segment
		ido=between(x(iseg(1)),x(iseg(length(iseg))),x0);

		if(~isempty(ido) & ido ~= 0 )
			y0(ido)=lint(x(iseg),y(iseg),x0(ido));
		end
	end
end