`NormalTransform` and `LognormalTransform`
I found the functions around
correlated_fields.py quite handy, so I moved them to a separate file and exposed them in the NIFTy namespace:
ift.NormalTransformfor the OpChain that transforms standard normally distributed values to normally distributed values
ift.LognormalTransformfor the OpChain that '...' to log-normally distributed values with given mean and std
ift.utilities.lognormal_momentsto calculate parameters for gauss(x, m, sig) so that exp(gauss(x, m, sig)) has the given mean and std. Used in
ift.LognormalTransform, but also useful for calculating prior values for lognormal models.
ift.utilities.value_reshaper: helper to make arrays of shape
(N,)from scalars and arrays of length one.
Also added tests for the transforms.