I use gcc 4.7.1

Enabling  OpenMP  option makes  my  6  core CPU  busy  on  all 6  of  them.
Surprisingly on Time x Velocity = 10000 x 10 grid it takes longer them with
disabled OpenMp option and only single core working. I have got 230 seconds
vs 160 seconds. Besides optimizing wisdom of FFT takes forever with OpenMP.


on a grid Time x Velocity = 10000 x 100
with OpenMP execution time = 988 seconds
without                    = 1708 seconds 

with 4 thread
on a grid Time x Velocity = 10000 x 100
with OpenMP execution time = 1036 seconds
without                    = 1603 seconds