Defining the semantics for a lazy array context

[kaushikcfd]

Background

• Lazy Array framework we will be using: github.com/inducer/pytato
• Lazy Array Context requires a context for symbolic operations (i.e. Pytato.Namespace) and an execution context. (probably a PyOpenCL command queue).
• Compile is a new operation that needs to be supported by ArrayContext. ArrayContext.compile would take a python callable, f, and return a JIT-ed function corresponding to f.

Looking at PyOpenCLArrayContext

• freeze: gets rid of the array context's queue, giving the caller the freedom to operate on the frozen array without being wary of the actx's state.
• thaw: attaches the array context's queue to the array, so any operations on the array are enqueued onto actx's queue.
• compile: takes a python callable and just returns the python callable.

Proposal: PytatoPyOpenCLArrayContext

• Uses pytato for lazy evaluation and any valued arrays are represented via pyopencl arrays.
• freeze: takes a Union[pytato.Array, pyopencl.array] and returns a pyopencl.array without the actx's queue.
• thaw: takes a pyopencl.array and returns a pytato.DataWrapper with the actx's namespace and queue attached to the cl array.
• compile: takes a callable and a numpy object array of DofArrays of pyopencl arrays and returns a A: CompiledOperator that would have a method A.__call__(self, x: np.ndarray[DofArray[PyOpenCLArray]]) -> np.ndarray[DofArray[PyOpenCLArray]]. The pyopencl arrays fed into and out of A.__call__ would still have the actx's command queue.

[inducer]

would take a python callable,

• Required to be pure, i.e. side-effect free
• Required to be operating on arrays
• Probably a few more requirements that we should map out exactly

return a JIT-ed function

Returns a "potentially more efficient" version of the function. (Returning f itself is valid.)

Terminology: "Operator" is very FEM-specific. CompiledArrayFunction?

I agree with the semantics you give.

[matthiasdiener]

This issue appears to be what was actually implemented in Pytato/Arraycontext.

[inducer]

Yep, I think it's good to close.

[kaushikcfd]

Yep it was, closing this one.