# linear system problem

e70443@estudiante.uam.es e70443@estudiante.uam.es
Thu Jan 29 15:14:00 GMT 2004

```Dear sirs,
I am a student of Computer Engineering at Madrid
University, Spain.
First of all I want to congratulate you for the
very useful "Scientific Library GSL" you have.

The matter that concerns me is:

I need to solve the linear system A x = b, where A
is a rectangular M-by-N matrix, and M > N. Looking the
functions of the library, I decided to use de QR descomposition.
Before any calculation, I create the A matrix and b vector view, the 'x'
and 'tau' vectors of N size, and the 'residual' vector of M size.
First, I call the function gsl_linalg_QR_decomp() with the matrix A and
the vector 'tau'. Then I call the gsl_linalg_QR_lssolve() function with
the arguments A (with the QR descomposition created by the previous
function), tau, b, x, and residual, to find the solution to the linear
system.
IÂ´m almost sure that these equations are correct but
the solution is not.
What should I expect ?
My question is; am I either using the right functions, or puting them in
the right order?
Shall I use another kind of descomposition?

Thank you very much for your cooperation

Sincerely,
Jaime Carsi Jaudenes.

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