# [Trilinos-Users] problem computing eigenvalues with Sundance

benk benk at in.tum.de
Thu Feb 2 15:28:36 MST 2012

```Dear Andrea,

Try
Expr massExpr = vx*ux + vy*uy + 0.0*q*p;
Expr massExpr = Integral( interior, vx*ux + vy*uy + 0.0*q*p, quad2);
This should cure the problem.
Sundance internally creates the Integral object.

Best Regards,
Janos

On Thu, 2012-02-02 at 21:39 +0100, Andrea Penza wrote:
> Dear all,
>
> I have been trying for days to solve the eigenvalue problem related to
> Navier-Stokes equations in primitive variables using Sundance. Here is
> the formulation that brings me troubles.
>
> // --------------------------------------------------------
>   bool lumpedMass = false;
>
>   BasisFamily L1 = new Lagrange(1);
>   BasisFamily L2 = new Lagrange(2);
>
>   Expr ux = new UnknownFunction(L2, "ux");
>   Expr vx = new TestFunction(L2, "vx");
>
>   Expr uy = new UnknownFunction(L2, "uy");
>   Expr vy = new TestFunction(L2, "vy");
>
>   Expr p = new UnknownFunction(L1, "p");
>   Expr q = new TestFunction(L1, "q");
>
>   Expr u = List(ux, uy);
>   Expr v = List(vx, vy);
>
>   // U is the solution of main flow, previously computed:
>   Expr U = List(u0[0], u0[1]);
>
>   // Define the new weak form for the operator A:
>
>   Expr eqn4 = Integral( interior, (dx*ux + dy*uy) * q, quad2 );
>
>   Expr eqnEig = eqn3 + eqn4;
>
>   // Define the weak form to build the operator M:
>   Expr massExpr = Integral( interior, vx*ux + vy*uy + 0.0*q*p, quad2);
>
>   LinearEigenproblem probEig(mesh, eqnEig, massExpr, List(vx, vy, q),
> List(ux, uy, p), vecType, lumpedMass);
> // -------------------------------------------------------------
>
> The compilation of the whole code ends fine.
> Trying to run the executable the system reports this error:
>
>
> 	Sundance detected exception:
> 	/home/andrea/Projects/trilinos-10.8.3-Source/packages/Sundance/src-core/InternalExprs/SundanceSymbPreprocessor.cpp:221:
>
> 	Throw number = 1
>
> 	Throw test that evaluated to true: e==0
>
> 	Non-evaluatable expr Sum of Integrals[
> 	Integral[
> 	rqc=Integration Region
> 	[6]            cell filter=MaximalCellFilter
> 	[6]            watchpoint=[]
>
> 	expr=vx*ux+vy*uy
> 	]
> 	]
>  	given to SymbPreprocessor::setupExpr()
> 	test FAILED
>
>
> Has anyone the idea of what could be the problem?
> Kind regards,
>
> Andrea
>
>
>
>
>
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>

```