Question

If there are N grid points in both the x and y-directions, how many times does the ADI scheme use the Thomas algorithm?

(a) N/2

(b) 2

(c) N^2

(d) 2N

This question was posed to me by my college professor while I was bunking the class.

The origin of the question is CFD Techniques topic in portion Some Simple CFD Techniques of Computational Fluid Dynamics

Answer 1

Right option is (d) 2N

The explanation is: In the first step of the ADI scheme, the Thomas algorithm is used N times to solve in the x-direction. Similarly, in the y-direction, again the Thomas algorithm is used N times to get the solutions. Totally, the Thomas algorithm is used 2N times.