Some refactorings.

move F out of the loop

node_xs as 2-array of global dim vectors. rename

eliminate node var unused

Extract i from Df

Extract Df out of comp loop

Extract Df and f out of node loop

Extract l and l_original_norm out of f, Df

local rhs stride

Block operations. Local x, node_local_indices

the latter is the key for all node 0/1 specific operations