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## [Getfem-users] Build a transport equation with the generic procedure

**From**: |
sébastien janas |

**Subject**: |
[Getfem-users] Build a transport equation with the generic procedure |

**Date**: |
Fri, 16 Apr 2010 13:40:59 +0200 |

Hi,
I try to solve a transport equation with getfem.
I have problem to deal with the term
div ( RHO * Y * U )
where
- div is the divergence
- RHO is the density
- Y is a moisture content
- U is the velocity
I try to build the matrix
(PSI_x^i * RHO * U_x * PSI^j ) +
(PSI_y^i * RHO * U_y * PSI^j ) +
(PSI_z^i * RHO * U_z * PSI^j )
where - PSI_a^b are the derivative of the base functions at nodes b in
respect to ditection a
- PSI^b are the base functions at nodes b
- U_a are the a components of velocity
In my program, I have the product RHO*U in a (nb_dof x 3) array, and I
construct my matrix like this
D = gf.asm_volumic('a=data(#2); M(#1,#1)+=
sym(comp(Grad(#1).Base(#1).Base(#1))(:,i,:,k).a(i,k))',mim,mf_u,mf_d,DATA)
where mf_u is
mf_u = gf.MeshFem(m,1)
mf_u.set_fem(gf.Fem("FEM_PK(3,1)"))
and mf_d
mf_d = gf.MeshFem(m,3)
md_d.set_fem(gf.Fem("FEM_PK(3,1)"
My questions are these
-> Is it the correct way to solve a transport equation ?
-> Is anybody have an exemple of such equation ?
-> With the exemple above, I get the following error that I don't
understand, is there somebody who can explain it to me ?
"wrong number of indexes for the 2th argument of the reduction
comp(Grad(#1).Base(#1).Base(#1))(:,i,:,k).a(i,k) (ranges=[0..12])"
Thanks a lot for your help,
Best regards,
Sébastien Janas

**[Getfem-users] Build a transport equation with the generic procedure**,
*sébastien janas* **<=**