If we use Mathematica notation the following works:
Div[Grad[u[x, y], {x, y}], {x, y}]
also if we multiply the gradient with a scalar:
Div[scal[x,y] Grad[u[x, y], {x, y}], {x, y}]
But when I use graphical mathematical notation with the Del operator (EscdelEsc), the first still works, but the second screws up (sorry, I can not paste the input here, because if I paste the graphical input it gets translated into: Subscript[\[Del], x, y]
what is interpreted differently in Mathematica ). I denote therefore the operator symbolically by: delxy
:
delxy.(scal[x,y] delxy u[x,y])
This gives an error message, complaining that one can not take the divergence of a scalar. Obviously scal[x,y] delxy u[x,y]
is considered a scalar.
Does anybody have an explanation and possibly a way around for this?
∇
can be used in this way, but "because if I paste the graphical input it gets translated into:Subscript[\[Del], x, y]
" seems to suggest that you're not making it correct in 1st case, either. Perhaps you can create a GIF to illustrate what you've done? $\endgroup$