Parallel computations of the finite difference approximation to the neutron diffusion equation, especially for three-dimensional problems, are investigated in anticipation of the use of high-speed vector computers such as the CRAY-1. Several general methods of solution of the seven-point formula are numerically studied from the viewpoint of the feasibility of their simultaneous calculations on vector computers. The time required for diffusion calculations can be reduced by a factor of 3 through vectorizing the inner iteration by the multidimensional ADC code. It is found that a checkerboard ordering in the overrelaxation method and a recently developed modified SLOR method avoid the degradation of convergence in vector iterations compared with traditional SOR and SLOR.
