Clarify the definiton of what grad() does.
Clarify the definiton of what grad() does.

abergeron/ccw_tutorial_theano,lisa-lab/tutorial_theano,lisa-lab/tutorial_theano,nouiz/ccw_tutorial_theano,mendax-grip/ccw_tutorial_theano,nouiz/ccw_tutorial_theano,abergeron/ccw_tutorial_theano,mendax-grip/ccw_tutorial_theano