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//Convolution Matrix
//convmtx(h,n) returns the convolution matrix for vector h. If h is a
//column vector and X is a column vector of length n, then convmtx(h,n)*X
//gives the result of the convolution oof h and X.If R is a row vector and X//is a row vector of length N, then X*convmtx(R,N) gives the convolution of R and X.
//Example:
//Generate a simple convolution matrix.
//
// h = [%i 1 2 3];
// convmtx(h,7) //Convolution matrix
//
//Author
//Debdeep Dey
function t=convmtx(v,n);
n=double(n);
[mv,nv]=size(v);
v=v(:);
//put Toeplitz code inline
c = [v; zeros(n-1,1)];
r = zeros(n,1);
m = length(c);
x = [r(n:-1:2) ; c(:)];
cidx = (0:m-1)';
ridx = n:-1:1;
t = cidx(:,ones(n,1)) + ridx(ones(m,1),:); //Toeplitz subscripts
t(:) = x(t); //actual data
//t = single(t);
// end of toeplitz code
if mv < nv then
t = t.';
end
endfunction
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