[julia-users] applying non zero boundary conditions in FEM

[Nguyen Vinh Phu]

Hello all,

I am implementing a finite element solver in Julia. I have computed the 
stiffness matrix (as a sparse matrix K) and the force vector (F). I have 
some non zero boundary conditions on 
the unknown. In Matlab, here is what I do:

bcwt=mean(diag(K)); % a measure of the average size of an element in K
% used to keep the conditioning of the K matrix
udofs=fixedNode;           % global indecies of the fixed  displacements
f=f-K(:,udofs)*uFixed;  % modify the force vector
K(udofs,:)=0;
K(:,udofs)=0;
K(udofs,udofs)=bcwt*speye(length(udofs)); % put ones*bcwt on the diagonal
f(udofs)=bcwt*speye(length(udofs))*uFixed;
 U=K\f;

I implemented the above in Julia and I got several errors associated with 
the following

f=f-K(:,udofs)*uFixed;  % modify the force vector
K(udofs,:)=0;
K(:,udofs)=0;
K(udofs,udofs)=bcwt*speye(length(udofs)); % put ones*bcwt on the diagonal
f(udofs)=bcwt*speye(length(udofs))*uFixed;

I would appreciate very much if someone can help. Thanks.

Best regards,
Phu