[gmx-developers] using arrays of rvec[] (ie x, v, f, etc)

[Nathan Moore]

> On Tue, 5 Jul 2005, Nathan Moore wrote:
>
>>I've figured out a possible fix.  I've defined temp_x in the following
>> way,
>>
>>    rvec *temp_x = (rvec *) malloc(array_length * sizeof(rvec));
>>
>>and then copied the array contents with,
>>
>>for (i = 0; i < array_length; i++) {
>>        x[i][0] = temp_x[i][0];
>>        x[i][1] = temp_x[i][1];
>>        x[i][2] = temp_x[i][2];
>>    }
>>
>>Comments?
>
> It should be possible without any copying, if you do Nprocs MPI calls on
> array segments. Copying and mallocing will kill any gain in performnce.

Do you see an obvious way around the malloc?  I can't see a static
"num_atoms" value that will allow me to define the temp_x array
statically.  I could of course define external variables in the mvxvf.c
function:

   int temp_x_array_declared=0;
   rvec *temp_x;

and then inside the function delcare the array conditionally, ie

   extern int temp_x_array_declared;
   extern rvec *temp_x;
   if(!temp_x_array_declared) {
      rvec *temp_x = (rvec *) malloc(array_length * sizeof(rvec));
      temp_x_array_declared=1;
   }

but that starts to get really busy for anyone who wants to read the code
in the future.  Do you see another way around this malloc?

Nathan