minor changes on the distritution
added a parameter to the kernel to represent type of distribution
used; surprisingly impacted the performance
moved the timer into top_calc_driver
now passing distribution parameter by pointer to the kernel
passing numL as pointer to the kernel
inlined pick_mat in the kernel function; changed all the temporary
loop indices to local vars
experimented passing by pointer/value; added debugging lines to
verify the correctness of the kernel; worked fine