DCMG0 1: A multigrid code. DCMG0 1 is an extension of the multigrid program MG0 1 to solve the Helmholtz equation with Dirichlet boundary conditions by difference methods in general bounded domains Ω⊂R 2 with high accuracy. The extension is based on a defect correction principle. DCMG01 has been developed and tested in Fortran 77 (single precision) on a CDC CYBER 170 computer (48 bit mantissa).