Question

The absolute residual is calculated __________

(a) to overcome high values of residuals

(b) to decelerate the convergence process

(c) to overcome the sign problems in the actual residual value

(d) to increase the rate of convergence

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This is a very interesting question from Relaxation in section Discretization of the Source Term & Relaxation of Computational Fluid Dynamics

Answer 1

Right choice is (c) to overcome the sign problems in the actual residual value

For explanation: The residual may be a positive or a negative quantity. As the sign is not needed, the absolute value of the residual is found. If the absolute residual decreases with iterations, the solution converges.