gsl_blas_dgemv return a 0 vector when using a vector twice

[Alejandro Cruz-Marcelo <ac6@........>]

Hello
When using the function
gsl_blas_dgemv(CblasNoTrans,
                   1.0, A, x,
                   1.0, y)   
It seems that when the SAME vector is used in the place of both x and y, 
the program's output is a vector of 0's. That is, if the call of the 
function is
gsl_blas_dgemv(CblasNoTrans,
                   1.0, A, y,
                   1.0, y)   
then y becomes a vector of 0's and no error is produced, even though the 
operation A*y + y makes perfect sense. I believe that in the 
documentation there is no warning about using the same vector twice in 
the function.
I hope this helps,
Thank you,
Alejandro