Plot the residual over iterations for every PE

[soumyadipghosh]

This would be useful to study convergence. There can be a struct similar to comm_data_struct which stores the residuals over iterations for every PE. After the solver converges, it can be printed to a file. A python script can then be used to plot data.

[pratikvn]

The object local_residual_vector_out already stores the local residual norms. You would just need to print it out.

[soumyadipghosh]

Did this using local_residual_norm defined here

[pratikvn]

local_residual_vector_out also stores local_residual_norm for all iterations and all subdomains.