Re: [Help-gsl] Resizing vectors and matrices

[ake]

At 06:52 PM 9/14/2004, JDL wrote:
> You could look at how the C++ standard template library allows you to 
> increase the size of a vector. This uses two numbers: the size is what you 
> use and the capacity is what you have available. You can resize (change 
> the size) whenever you want. If the new size exceeds the capacity, you 
> create new vectors with capacity the first power of two bigger than the 
> new size, copy and reassign.

I have looked briefly at init_source.c in the block and vector directory of 
gsl-1.5, and it seems to me that all one needs to do is to add functions 
gsl_vector_realloc and gsl_block_realloc. The latter function should 
reallocate space for block->data and update block->size. Then 
gsl_vector_realloc calls gsl_block_realloc and makes appropriate changes if 
need to vector->data, vector->size and vector->block. That should be all, 
or have I missed something of importance?

Matrices seem more difficult since element (i,j) of an (m,n) matrix is 
identified from a vector as matrix->data[i * m + j], ignoring the fact that 
the physical size may differ from the actual size. Thus, increasing n to n 
+ k is straigtforward, just allocate k * m additional slots at the end of 
matrix->data, but increasing m is not trivial. It may be that the matrix 
has to be copied onto a new one of the appropriate size.

Sincerely,
Ake Brannstrom