symbolic_min(d::Dimension) needs to return devito.types.basic.Scalar

[jkwashbourne]

no working failing example, but this issue is seen when running an operator on CPU and GPU with and without the free surface boundary condition.

arch	free surface	notes
CPU	off	runs
CPU	off	runs
GPU	on	runs
GPU	on	fails

I do not know what is different about GPU run from CPU run, but the errors occur when I add indexed free surface boundary condition equations that reference symbolic_min of the z dimension.

zmin = symbolic_min(z)
@show typeof(zmin)

returns:

typeof(zmin) = PyCall.PyObject

this might not be the fix, but should likely be done anyway.

[jkwashbourne]

Note, an equivalent python only test works