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If you use nonanalytic functions in a complex-valued problem, such as real, imag, conj, abs, or arg.
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If you use the nojac operator.
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For time-dependent problems, the time-stepping algorithm must know if a problem is complex-valued. If your model uses a complex-valued initial solution, the COMSOL software detects this and classifies the problem accordingly. If the problem is complex-valued because of a complex-valued PDE coefficient or other material property, go to the Time-Dependent Solver node’s Settings window, and in the Advanced section select the Allow complex numbers check box.
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If you expect to receive complex outputs from real inputs in elementary functions such as sqrt, log, and asin, or when evaluating a nonintegral power of a negative number, add an Advanced subnode. Then in the Settings window under General, select the Allow complex-valued output from functions with real input check box. By default, the COMSOL software gives an error message if a real input to a function generates a complex output.
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