beam.k=[-1,0];
beam.origin=[2,0.5];
beam.face=NA;

face1.vertex1=[-1,0];
face1.vertex2=[1,0];
face1.n_right = 1;
face1.n_left= 1.5;

face2.vertex1=[1,0];
face2.vertex2=[0,1];
face2.n_right = 1;
face2.n_left= 1.5;

face3.vertex1=[0,1];
face3.vertex2=[-1,0];
face3.n_right = 1;
face3.n_left= 1.5;

faces={face1,face2,face3};


border1.vertex1=[-5,-5];
border1.vertex2=[5,-5];
border1.n_right = 1.;
border1.n_left= 1;

border2.vertex1=[5,-5];
border2.vertex2=[5,5];
border2.n_right = 1.;
border2.n_left= 1;

border3.vertex1=[5,5];
border3.vertex2=[-5,5];
border3.n_right = 1.;
border3.n_left= 1;

border4.vertex1=[-5,5];
border4.vertex2=[-5,-5];
border4.n_right = 1.;
border4.n_left= 1;

borders={border1,border2, border3, border4};
beams={beam};
beam_trace(beams, faces, borders )