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function b = convmtx (a, n)
//Calling sequence:
//b=convmtx(a,n);
//convmtx(a,n);
//This function returns the convolution matrix 'b'.
//If 'a' is a column vector and if we need the convolution of 'a' with another column vector 'x' of length 'n' then an operation "convmtx(a,n)*x" yeilds the convoluted sequence much faster.
//Similarily, if 'a' is a row vector then to convolve with another row vector 'x' of length n , then convoluted sequence can be obtained by
//x*convmtx(a,n)
[nargout,nargin]=argn();
if (nargin ~= 2)
error("wrong number of input arguments");
end
[r, c] = size(a);
if ((r ~= 1) & (c ~= 1)) | (r*c == 0)
error("convmtx: expecting vector argument");
end
b = toeplitz([a(:); zeros(n-1,1)],[a(1); zeros(n-1,1)]);
if (c > r)
b = b.';
end
endfunction
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