Value of num_params in the disc classes

[bartgol]

I think we should store num_params in more fine-grain detail in the disc classes. Right now, the disc factory stores this as the sum scalar+distributed. However, this value is later used by the disc classes as the domain dim of dxdp. While this is in principle correct, we never do this for distributed params. That is, we never store a multivector with distributed domain (we can't!).

So I wonder if we should make the disc classes

• store two values: num_scalar_params and num_dist_params?
• store num_params as the number of scalar params?
• something else?

@mperego you may have an opinion on this, or perhaps correct a flaw in my understanding.