Fortran

Additional code snippets and notes can be found at RMeli/fortran-playground.

ScaLAPACK

numroc

numroc computes the NUMber of Rows Or Columns of a distributed matrix owned by the process indicated by iproc. Trying to use numroc in a Fortran program, results in the following error:

   61 |     m = numroc(n, 1, myrow, 0, nprow)
      |        1
Error: Function 'numroc' at (1) has no IMPLICIT type

In order to avoid this error, the function needs to be declared as external.

integer, external :: numroc

external statement

The external statement specifies procedures or dummy procedures as external, and allows their symbolic names to be used as actual arguments.

Busy Wait

subroutine busywait(wait_time)
   real(kind=dp), intent(in) :: wait_time ! (1)!

   real(kind=dp) :: t_start, t_now, elapsed_time

   elapsed_time = 0.0_dp

   call cpu_time(t_start)

   do while (elapsed_time < wait_time)
      call cpu_time(t_now)
      elapsed_time = t_now - t_start
   end do

end subroutine

1. Time to wait in seconds.