# 
# Numerical Mathematics and Computing, Fifth Edition
# Ward Cheney & David Kincaid
# Brooks/Cole Publ. Co.
# (c) 2004
#
# file:  ell
#
# Elliptic PDE
# 
with(linalg):
with(PDEtools):
pde := laplacian(u(x,y),[x,y]) - 0.04*u(x,y) = 0;
ans := pdsolve(pde);
pdetest(ans,pde);
f(x,y) := cosh(0.2*x) + cosh(0.2*y);
eqn := diff(f(x,y),x,x)+diff(f(x,y),y,y) - 0.04*f(x,y);
normal(eqn);