Turns on/off (default on) checking for values falling below the field warn threshold value after a nonlinear update. A summary is printed if any are found.
In Alamode the unknowns typically represent a concentration, and it is not physical to have negative concentrations. The nonlinear solution may compute negative concentrations due to overshoot. It is usually a good idea to adjust these values to avoid converging to an incorrect fixed point in the nonlinear solver.