empymod/emg3d: Complex sources

Krylov subspace solvers:

• Solver now finishes in the middle of preconditioning cycles if tolerance is reached.
• Solver now aborts if solution diverges or stagnates also for the SSL solvers; it fails and returns a zero field.
• Removed gmres and lgmres from the supported SSL solvers; they do not work nice for this problem. Supported remain bicgstab (default), cgs, and gcrotmk.

Various small things:

• New attribute Field.is_electric, so the field knows if it is electric or magnetic.
• New verb-possibility: verb=-1 is a continuously updated one-liner, ideal to monitor large sets of calculations or in inversions.

• The returned info dictionary contains new keys:

  • runtime_at_cycle: accumulated total runtime at each cycle;
  • error_at_cycle: absolute error at each cycle.

• Simple __repr__ for TensorMesh, Model, Fourier, Time.

Bugfixes:

• Related to get_hx_h0, data_write, printing in Fourier.