When using the Preconditioned CG solver, one should throw an exception when the preconditioner has not been set by the user, or have a default one set, because otherwise there is a segmentation fault further down the line in the operator usage which does not give any error information to the user.
When using the Preconditioned CG solver, one should throw an exception when the preconditioner has not been set by the user, or have a default one set, because otherwise there is a segmentation fault further down the line in the operator usage which does not give any error information to the user.