function matrix = matrip(A, B, C, J)

vectorlow = A(2:J);
diaglow = [zeros(1,J);diag(vectorlow),zeros(J-1,1)];
vectorup = C(1:J-1);
diagup = [zeros(J-1,1),diag(vectorup);zeros(1,J)];
matrix = diag(B(1:J))+diaglow+diagup;

return