RE: autoconf usage : -DHAVE_GSL ?

[Brian Gough <bjg at network-theory dot co dot uk>]

J.J. Gomez Cadenas writes:
 > For the wrapper classes that I am preparing (so far, complex, permutations,
 > vector & matrices) I would like to have the last version of GSL with your
 > last additions (LU and LU inverse for a complex matrix, etc). I am working
 > chiefly in Windows, this days. Would it be possible for you to create
 > another setup.exe with an updated version, some time?

Ok. I'll make one tomorrow.  Currently there's one on my webpage which
has 'inline' functions working, but doesn't have the complex LU.  I
haven't benchmarked it yet. In principle it should give improved
performance for some of the linear algebra.  The file size is much
larger though.

 > Concerning matrices. There is a typo in the documentation, pag 84, it should
 > say gsl_matrix_mul_element (and gsl_matrix_div_element) instead of
 > gsl_matrix_mul, which is very misleading (unless you read carefully the
 > title makes you believe it's the product of two matrices not the product of
 > the elements).

Thanks, now corrected.

 > Actually, you do not include the product of two matrices as matrix operation
 > but in linear algebra. Why? The product of two matrices is guaranteed to
 > exist, e.g, the matrix are a ring, so the operation is well defined. In the
 > same grounds that you include the addition of two matrices (matrices are a
 > group) I would tend to add the product.

I left out the matrix multiply because it is in BLAS, but matrix
addition is not so I provided that separately.  Strictly speaking the
'matmul' function in linalg is also obsolete.  At that time the blas
library was not finished so the matmul function was used.  Now that
the BLAS is complete I recommend using gsl_blas_dgemm for better
performance.

This doesn't cover multiplying of integer matrices, but it would seem
to be dangerous to multiply those as they could easily overflow.