The cov function in PyMC3 accepts numpy array, theano tensor, or pymc3 RV as input. You can only do inference on the RVs in general (with some twist you can do it on theano tensor as well)
The cov function in PyMC3 accepts numpy array, theano tensor, or pymc3 RV as input. You can only do inference on the RVs in general (with some twist you can do it on theano tensor as well)