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Compute the sparse QR factorization of a, using CSparse. As the matrix Q is in general a full matrix, this function returns the Q-less factorization r of a, such that r
= chol (a' *a).If the final argument is the scalar
0and the number of rows is larger than the number of columns, then an economy factorization is returned. That is r will have onlysize (a,1)rows.If an additional matrix b is supplied, then
spqrreturns c, where c=q' *b. This allows the least squares approximation of a\b to be calculated as[c,r] = spqr (a,b) x = r \ cSee also: spchol, qr.