How to use ConvolvFFTPower of fields other than FKP density?

[julianbautista]

First, thank you for all the work building this amazing package.

I read the cookbooks on

• how to paint the momentum with a fixed line-of-sight (L.O.S.), and
• how to compute multipoles of the density power-spectrum in a realistic survey with varying L.O.S.

I would like to:

• compute multipoles of the momentum power-spectrum with a varying L.O.S.

Looking at the code of ConvolvedFFTPower, it looks like it really requires a FKPCatalog or FKPCatalogMesh, which assume that I want the power-spectrum of F = w * (n_g - alpha * n_r).

The solution for my problem would be to be able to provide F = w * n_g * radial_velocity, and then give it to ConvolvedFFTPower for compute the multipoles with a varying LOS. This new definition of F does not require a random catalog, but I need the varying LOS capability of ConvolvedFFTPower.

Do you have any suggestions on solutions or alternative hacks I could use? I am new to this package, so apologies if the solution is obvious.

Many thanks

[rainwoodman]

Hi,

A very quick suggestion is to define a different CatalogMesh class, for example, FKPVelocityCatalogMesh. The implementation can be based on (mostly copying) FKPCatalogMesh. In FKPVelocityCatalogMesh.to_real_field, however, you can paint F = w * n_g * radial_velocity, rather than painting the traditional FKP field.

Because your data doesn't come with randoms, I would also suggest __init__ of FKPVelocityCatalogMesh consumes a Catalog object, instead of a FKPCatalog object (which is used by a FKPCatalogMesh.__init__).

What do you think?