Construct an eirpr object for an arbitary model

This takes a model and uses the XH component to define the eirpr relationship using `xde_scaling_eir` then calls `xde_scaling_lambda`

xde_scaling(model, N = 25, F_eir = NULL)

Arguments

model

a list that defines an `ramp.xds` model (*e.g.*, generated by `xde_setup()`)

N

the size of the mesh on aEIR

F_eir

a function to compute the EIR as a function of time