where
r^{2}=x^{2}+y^{2} .
SUBROUTINE TRIDAG(A,B,C,R,U,N) PARAMETER (NMAX=100) DIMENSION GAM(NMAX),A(N),B(N),C(N),R(N),U(N) IF(B(1).EQ.0.)PAUSE BET=B(1) U(1)=R(1)/BET DO 11 J=2,N GAM(J)=C(J-1)/BET BET=B(J)-A(J)*GAM(J) IF(BET.EQ.0.)PAUSE U(J)=(R(J)-A(J)*U(J-1))/BET 11 CONTINUE DO 12 J=N-1,1,-1 U(J)=U(J)-GAM(J+1)*U(J+1) 12 CONTINUE RETURN END
to 6 significant figures of precision. If you wish you may use Maple® or Mathematica® or Matlab® to check your work—or else multiply the matrix by the solution and see whether you obtain the inhomogeneous term.