Hi,

I want to assemble a restriction matrix to extract the DoFs on part of the boundary.

I know the interpolate function can assemble such matrix by providing two FE function spaces. Can we define a P1 function space on one side of the unit square? then interpolate it to the P1 function space on the unit square?

see attached code.

Best regards,

Shihua

// Mesh

mesh Th = square(4, 4);

plot(Th, wait=true);

// Fespace

fespace Vh(Th, P1);

// Fespace on one edge of unit square

meshL Eh=segment(4); //

fespace EVh(Eh , P1);

// interpolate matrix from

matrix Rt;

Rt = interpolate(Vh,EVh,inside=true);