The Krylov solvers such as scipy.sparse.linalg.cg have the callback argument. I am using this to monitor convergence. According to the docs, for scipy.sparse.linalg.cg the input given to the callback is the solution vector and for scipy.sparse.linalg.gmres it is the residual vector. But in my version 0.17.1 scipy.sparse.linalg.gmres returns a float. I guess it is the 2-norm of the residual vector. Shouldn't the input given to callback be independent of the Krylov method?