`pm.gp.util.stabilize` needs a docstring with usage instructions

[michaelosthege]

with pm.Model():
    cov = pm.gp.cov.ExpQuad(input_dim=2, ls=1)
    cov = pm.gp.util.stabilize(cov)

AttributeError                            Traceback (most recent call last)
<ipython-input-44-f4041194b996> in <module>
      1 with pm.Model():
      2     cov = pm.gp.cov.ExpQuad(input_dim=2, ls=1)
----> 3     cov = pm.gp.util.stabilize(cov)

~\AppData\Local\Continuum\miniconda3\envs\murefi_env\lib\site-packages\pymc3\gp\util.py in stabilize(K)
     38 def stabilize(K):
     39     """ adds small diagonal to a covariance matrix """
---> 40     return K + 1e-6 * tt.identity_like(K)
     41 
     42 

~\AppData\Local\Continuum\miniconda3\envs\murefi_env\lib\site-packages\theano\tensor\basic.py in identity_like(x)
   2922 
   2923 def identity_like(x):
-> 2924     return eye(x.shape[0], x.shape[1], k=0, dtype=x.dtype)
   2925 
   2926 

AttributeError: 'ExpQuad' object has no attribute 'shape'

Versions and main components

• PyMC3 Version: 3.11.2 (did not check with main)
• Aesara/Theano Version: 1.1.2

[bwengals]

I think its OK, because pm.gp.util.stabilize acts on tensors, not covariance functions (AttributeError: 'ExpQuad' object has no attribute 'shape'). Maybe it should also act on pm.gp.cov.Covariances? But in that case you can add a WhiteNoise covariance. Either way the docstring could probably use more detail.