NmtField lmax or lmax_mask negtive don't work

[carlosggarcia]

This code fails:

f = nmt.NmtField(m, None, spin=0, lmax_mask=-1)

(also for lmax), with error. If it is intentional, the documentation needs to be updated.

File ~/mambaforge/envs/tjpcov/lib/python3.12/site-packages/pymaster/field.py:185, in NmtField.__init__(self, mask, maps, spin, templates, beam, purify_e, purify_b, n_iter, n_iter_mask, tol_pinv, wcs, lmax, lmax_mask, masked_on_input, lite, mask_22, mask_12)
    183 if lmax_mask is None:
    184     lmax_mask = self.minfo.get_lmax()
--> 185 self.ainfo = ut.NmtAlmInfo(lmax)
    186 self.ainfo_mask = ut.NmtAlmInfo(lmax_mask)
    188 # Beam

File ~/mambaforge/envs/tjpcov/lib/python3.12/site-packages/pymaster/utils.py:452, in NmtAlmInfo.__init__(self, lmax)
    450 m = np.arange(self.mmax+1)
    451 self.mstart = (m*(2*self.lmax+1-m)//2).astype(np.uint64, copy=False)
--> 452 self.nelem = int(np.max(self.mstart) + (self.lmax+1))

File ~/mambaforge/envs/tjpcov/lib/python3.12/site-packages/numpy/core/fromnumeric.py:2810, in max(a, axis, out, keepdims, initial, where)
   2692 @array_function_dispatch(_max_dispatcher)
   2693 @set_module('numpy')
   2694 def max(a, axis=None, out=None, keepdims=np._NoValue, initial=np._NoValue,
   2695          where=np._NoValue):
   2696     """
   2697     Return the maximum of an array or maximum along an axis.
   2698 
   (...)
   2808     5
   2809     """
-> 2810     return _wrapreduction(a, np.maximum, 'max', axis, None, out,
   2811                           keepdims=keepdims, initial=initial, where=where)

File ~/mambaforge/envs/tjpcov/lib/python3.12/site-packages/numpy/core/fromnumeric.py:88, in _wrapreduction(obj, ufunc, method, axis, dtype, out, **kwargs)
     85         else:
     86             return reduction(axis=axis, out=out, **passkwargs)
---> 88 return ufunc.reduce(obj, axis, dtype, out, **passkwargs)

ValueError: zero-size array to reduction operation maximum which has no identity

[carlosggarcia]

It might be related with this error. I believe that the check lmax <= 0 is not working at all. It seems that for lmax=0it actually computes it up to l=0

I got this error when I set lmax = 0 in the field and reuse a precomputed covariance workspace

    def comp_gaussian_covariance(cw, spin_a1, spin_a2, spin_b1, spin_b2, wa, wb, ncl11, ncl12, ncl21, ncl22, dout):
>       return _nmtlib.comp_gaussian_covariance(cw, spin_a1, spin_a2, spin_b1, spin_b2, wa, wb, ncl11, ncl12, ncl21, ncl22, dout)
E       RuntimeError: Coupling coefficients only computed up to l=0, but you requirelmax=95. Recompute this workspace with a larger lmax

[damonge]

@carlosggarcia I think this is a problem with the documentation. If you want to use the default lmaxs, you should set them to None, which is the default. Does that make sense? I'll open a PR to fix the docs.