[Nek5000-users] opdiv and multd

[nek5000-users at lists.mcs.anl.gov]

Hi all,

I am having some problems using the subroutines opdiv and multd.
For some reasons they do not give me correct results.
Do they need any special treatment or precautions?

I was trying to compute the divergence of a 3D field, and i realized 
that in my case the multd subroutine used
by opdiv does not gives good results, while the same derivative computed 
from gram1 gives no problems.

For example, I overwrite an analytical field :

          ...
          parameter(lt=lx1*ly1*lz1*lelt)
          real       Res(lt)
          ...
                     vx(i,j,k,e)=   1.0*sin(x)*cos(y)*cos(z)
          ...
              call print_line(vx)
          ...
          iflg = 1
          call multd (RES(1),vx,rym2,sym2,tym2,2,iflg)
             call print_line(Res(1) )

         call gradm1(work1,Res(1),work2,vx)
             call print_line(Res(1) )
          ...
          if (lx2.ne.lx1) then
          ...
          STOP
          endif


and  print output a (xr,:,zr) the result  (performed by print_line) .
In vxi.eps i compare the result (lines) with the analytical solution( 
symbols). The result of multd is not correct while all
the others match perfectly the analytical solution.
In vxy.eps i plot only the result of multd. Note that on y i have 12 
elements the same number of peaks of the solution.

Does anybody have an idea on how to fix this?

Thank you very much for any help or suggestion

francesco



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