mistake on exp_D

[TomFD]

Hi, for the symmetric split-step, the linear step is currently set as:
A[:] = self.LinearStep(A,dz,direction)
However, is uses
self.Calculate_expD(h,direction)
and there:
self.exp_D[:] = np.exp(directionh0.5*(1j*self.betas-self.alpha/2.0))
In my opinion, the 0.5 is a mistake.
It actually works for the RK4IP implementation, because there, the first step is only dz/2. Currently it is done by
self.A_I[:] = self.LinearStep(A,h,direction)
but should be something like: self.A_I[:] = self.LinearStep(A,h/2.0 ,direction)
if the LinearStep is corrected.

You can check that there are different results when replacing the method for simple problems
evol.method=SSFM.SSFM.METHOD_SSFM
#evol.method=SSFM.SSFM.METHOD_RK4IP

as well as the dispersion parameter D tells you by its value for linear propagation, how the pulse should spread, but it does only half its value.

cheers, Tom

[pyNLO]

Thanks for reading through the code so carefully. You are entirely correct.