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function [y]=interpln(xyd,x)
//Given a set of points in the plane with coordinates xyd and a set of
//x points
// [y]=interpln(xyd,x) allows to compute a set of y obtained by linear interpolation.
//% parameters
// xyd : coordinates of points (2 rows matrix)
// first row : x
// second row : y
// x : vector of x's for which y is wanted
// y : vector of y computed.
//!
// S Steer INRIA 1991
// Copyright INRIA
[md,nd]=size(xyd);
if md<>2 then
error('interpln:xyd must have two rows!')
end
//
n=size(x,'*');
d=xyd(:,1:nd-1)-xyd(:,2:nd);
k=find(abs(d(1,1:nd-1))==0)
if k<>[] then
d(1,k)=%eps*ones(k)
xyd(1,k+ones(k))=xyd(1,k)+%eps*ones(k);
end
d=d(2,:)./d(1,:);
for pt=1:n,
xpt=x(pt);
k=find(xpt>xyd(1,1:nd-1)&xpt<=xyd(1,2:nd));
if k==[] then
if xpt<=xyd(1,1) then k=1,else k=nd-1,end
else
k=k(size(k,'*'));
end
y(1,pt)=xyd(2,k)+(xpt-xyd(1,k))*d(k)
end
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