Using the Code $2$ given in Kundu et al$.,$ for two$-$dimensional unsteady linear advection$-$

diffusion equation, re$-$solve the defined problem with:

a$)$ Only diffusion.

b$)$ Only advection $($make sure that the results look physically correct, that means you

may need to add nearly zero diffusion to the equations for stability$).$

Show the modifications made; and discuss and submit the results.