How use scalar type and complex type at the same time?

[Zhifeng Sheng]

Dear all

I am working on a FEM program, which can be used to solve time domain 
and frequency domain EM problems. I finished the time domain solver part 
and now I need to implement the frequency domain solver.... So I built 
Petsc with --scalar-type = complex, and then my time domain solver can 
not be compiled, it says " can not convert double to PetscScalar".

Is there any way that I can handle both real matrix and complex matrix 
at the same time? (without changing my old code too much?)

Thanks
Best regards
Zhifeng Sheng