James Van Buskirk wrote:

>>r(0,:)    = rhub
>>r(nr+1,:) = rmax
>>dt(0,:)   = 0.0
>>dft(0,:)  = 0.0
>>dfr(0,:)  = 0.0
>>dt(nr+1,:)   = 0.0
>>dft(nr+1,:)  = 0.0
>>dfr(nr+1,:)  = 0.0
>>I found the execution time of the latter to be higher than the former,
>>as if many DO loops were executed instead than just one. Why use
>>global array operations then? Isn't better to stick to old plain DO
>>loops? Thanks,
> Normally an initialization loop like this one would be faster as
> separate loops than one fused loop because it's faster to access
> memory consecutively rather than jumping around as implied by the
> fused loop.  However in this case the loops appear to be setting
> boundary values so they are traversing rows rather than columns of
> the arrays.  As a consequence the code jumps around in memory no
> matter what the compiler does and loop fusion can win out because
> it implies less loop overhead which otherwise would be of negligible
> importance compared to memory access considerations (assuming that
> the data set is too large to fit in cache).

> One thing to investigate is whether the r(i,j), dt(i,j), dft(i,j),
> and dfr(i,j) always get accessed together.  If so, you could group
> them as a derived type and the above loop could go 4X as fast as
> the structure of arrays code listed above.