Question

If N is the number of unknowns, the number of operations required for backward substitution is ____________

(a) \(\frac{N^3}{3}\)

(b) \(\frac{N^3}{2}\)

(c) \(\frac{N^2}{2}\)

(d) \(\frac{N^2}{3}\)

I had been asked this question during an interview.

Query is from Numerical Methods in portion Numerical Methods of Computational Fluid Dynamics

Answer 1

Correct choice is (c) \(\frac{N^2}{2}\)

Best explanation: The number of operations required for the overall Gauss elimination method is \(\frac{N^3}{3}\). The number of operations for backward substitution is \(\frac{N^2}{2}\). This high computational cost is the disadvantage of the Gauss elimination method.