# Mathematica derivative

• Mathematica

## Main Question or Discussion Point

Mathematica:

Code:
In[1]:= x = {(u + 2 v)/3, (u - v)/3, w}; D[x[u], u]

Out[1]= {1/3, 1/3, 0}[u] + {(u + 2 v)/3, (u - v)/3, w}’[u]
Why does it do this? Wolfram Alpha gives the answer I expected:

http://www.wolframalpha.com/input/?i=d%2Fdu+%28{%28u+%2B+2+v%29%2F3%2C+%28u+-+v%29%2F3%2C+w}%29

{1/3, 1/3, w’(u)} = {1/3, 1/3, 0} if w doesn't change with u.

Related MATLAB, Maple, Mathematica, LaTeX News on Phys.org
You defined
x = { ... }
without reference to u. So x was stored as { ... }.
Then you tried taking the derivative of x, which gets converted to
{ ... }
which doesn't make sense. If you ask for D[x,u] you will get what you wanted.

Wolfram Alpha has a more flexible grammar -- ie it's not a programming language.
Thus it guessed what you meant.

Thanks, Simon. Problem solved. Yes, I've noticed before that WA is more forgiving and able to guess (for better or worse) at the meaning of ambigious syntax.