Time splitting issue

[charlotte_M_]

 Hello Everyone,

I'm trying to solve a problem use time splitting method.  For this i have to solve linear systems  of equation using tridag (fortran ) routine.

I have two problems

The first one is that the coefficients  use in tridag are 2 D array while this routine use 1 D array.

What i did to overcome this is the following (just a example):

  do  k=1,NT         ! Main loop over the time step

!Compute  the solution of the first equation 

do i=1, N1

do j= 1, N2

   A(j) = x(i)*y(j)

  B(j)= x(i)*y(j)

  C(j)=x(i)*y(j)

 End do 

 Call tridag( A,B,C,F0, F1, N)     !F0  is a two dimensional function , F1, a one dimensional function

 End do 

!Once done i will use F1 as the initial condition for the second equation

 Do j =1, N2

 Do i=1,N1

  E(i)= xx(i)*y(jj)

 F(i) =xx(i)*yy(j)

 G(i)= xx(i)*yy(i)

End do 

  Call tridag(E,F,G,F1,F2,n1)

end do 

!Next step Write result in the file, for different time

!Finally   i update my initial condition

   DO i=1,N1

 DO j=1,N2

   F0(i,j) =F2(i,j)

  end do

end do

END DO         !ENd of the time loop

****** The second  problem is that , i have the same result for different  time that i print the solution.

 I am doing something wrong?

 sorry for the long text

  Thank you

[jimdempseyatthecove]

For parallelization, consider the following untested code:

!$omp parallel
!$omp master
do  k=1,NT         ! Main loop over the time step
  !Compute  the solution of the first equation
  do i=1, N1
    !$omp task firstprivate(i) private(j)
    do j= 1, N2
      A(j) = x(i)*y(j)
      B(j)= x(i)*y(j)
      C(j)=x(i)*y(j)
    End do 

    Call tridag( A,B,C,F0(i,:), F1(i,:), N)     !F0  is a two dimensional function , F1, a one dimensional function
    !$omp end task
  End do
  !$omp taskwait
  ! *** Note, on prior iteration (after first iteration)
  ! *** a task was enqueued (and may have been pending) to write the results
  ! *** of the prior iteration's F2. The above taskwait will also wait for
  ! *** that task to complet, thus freeing up the use of F2 for this iteration.

  !Once done i will use F1 as the initial condition for the second equation
  Do j =1, N2
    !$omp task firstprivate(j) private(i)
    Do i=1,N1
      E(i)= xx(i)*y(jj)
      F(i) =xx(i)*yy(j)
      G(i)= xx(i)*yy(i)
    End do 
    Call tridag(E,F,G,F1(:,j),F2(:,j),n1)
    !$omp end task
  end do 
  !$omp taskwait

  !$omp task private(i,j) ! and any other conflicting variables
  !Next step Write result to the file, for different time
  ...
  !$omp end task
  ! *** Note, the write task will be in progress during the next iteration of k's computation
  ! *** of the first tridag

  ! Now update F0 for initial condition for next time step
  F0 = F2
END DO         !ENd of the time loop
! *** now wait for the last write of F2
!$omp taskwait
!$omp end master
!$omp end parallel

Jim Dempsey

[jimdempseyatthecove]

Also, if the timestep (k) is to be written to the output file, then make it firstprivate(k) on the task that performs the write.

Jim Dempsey