Static shapes

Description

From this discussion on pymc discourse, "static shapes are quite recent and we are still updating Ops to reflect them when possible." -@ricardoV94

Is help still needed with ensuring static shape output from Ops where possible? If so - here's a quick (obviously incomplete!) start on listing out ops to work on.

No static shape output (todo):

• Eye
• conv ops (#150)

No static shape output (and perhaps to remain as such):

• Subtensor (indexation)

Could fail earlier:

• Dot: outputs correct static shape if the input shapes align, but outputs incorrect static shape if input shapes are wrong. Error at eval time
• SpecifyShape: similar to Dot. ptt.specify_shape(np.ones((2,3)), shape=(3,3)).type # tensortype shape (2,3)

Recently addressed:

• Join #164
• MaxAndArgmax #206

Hopefully this is the right place to start the discussion. If help is wanted, I would appreciate some guidance on how to go about this in a more principled way -- where/how to look, what a fix might look like, etc -- and of course any other suggestion on Ops that don't yet support static shape output.

Start with the linked PyMC Discourse discussion and the listed Ops: Eye, conv ops, Subtensor, Dot, and SpecifyShape; compare them with the recently addressed Join and MaxAndArgmax issues (#150, #164, and #206). The issue needs a decision on which gaps are actionable and what correct static-shape behavior means before implementation can be considered done.