Material output in blueprint

we all know that there are easy ways of sending parameters to materials, but is there a way to return or populate a variable that can be accessed via blueprints ?

the good point of it is that then some calculation can be ported to the GPU and the result comes back to a blueprint.

Not sure what you mean. Are you talking about using the compute shader from bluprints?
I don’t think we have a node for that. But you could write the CS code in C++ and expose the function to BP.
Take a look at FGlobalShader. I think you can create a compute shader by extending it

For anyone still encountering this problem, here is what you could do: Passing Texture/Material from Material to Blueprint - Asset Creation - Unreal Engine Forums