Read matlab matrix into fenics

Question

Hello
I want to read a vector/matrix "B" that is saved by matlab into fenics. In my fenics python program I want to read this matrix and compute

B*u

where u is a Function. I want to use B*u as boundary condition in a PDE.

I can read matrix using scipy.io. How can I form the product B*u ?

Thanks

Comments

Can you make it more clear to me, how and where you want to apply B. In particular, if u is a function, what should be the product of B and u?

Answer 1

If B is a matrix with the same dimension as the number of
degrees of freedom in u,
you can take B*u.vector().array().
Then you let numpy do the matrix vector product.

If you want to let dolfin perform the matrix vector product you
would have to make a dolfin matrix out of B.

If B is a matrix with pointwise values then you should use
B in an Expression.