[Help-gsl] gsl_vector_get () return status

[Joel J. Adamson]

Howdy,

Using gsl_vector_get (), how do I distinguish between an error accessing
an out-of-range vector element (returns 0 with error checking off) and
an element that is genuinely 0?

I am programming in Gambit-C (Scheme->C compiler) using the GSL for
linear algebra.  The gsl_vector and gsl_matrix operations have worked
really well for me, however I have a unique problem: I need to know when
to stop assigning vector elements to a vector in Scheme.  If I can
determine the length of the vector somehow in C, then I could simply
allocate the length in the Scheme code and stop at that index.  I
thought to do this with error checking: iterate up the vector elements
until I reach an out-of-range element, however I have the above
problem of distinguishing an element 0 from an error code 0.

Is there a way to either (a) determine the length of the vector in C or
(b) determine the error condition?  Is there some other variable that
gets set (errno?) when the error occurs?  I'm fairly new to C, and none
of the books I have adequately explain how to obtain return status (is
it anything other than the return value of the function?).

Or should I just use the BLAS functions and abandon gsl_vector and
gsl_matrix?

Thanks for any help you can offer,
Joel
-- 
Joel J. Adamson
Biostatistician
Pediatric Psychopharmacology Research Unit
Massachusetts General Hospital
Boston, MA  02114
(617) 643-1432
(303) 880-3109

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