What does the (∂X) symbol means in Matrix Cookbook?

Question

Check page 8 and equation 34 of Matrix Cookbook.

In this simple case we take the derivative of a matrix that is multiplied by a constant and we have: $\partial (aX) = a*(\partial X)$

Probably missing something crucial because I would expect ∂aX/∂X = a

So what does (∂X) represents exactly?

You did not faithfully reproduce equation (34). And that difference is crucial to your question. The LHS is a differential, not a derivative. — Mark L. Stone, Dec 15 '17 at 20:10

score 0 · Accepted Answer · answered Dec 15 '17 at 21:06

0

The notation:$$\partial (aX) = a*(\partial X)$$ is referred to ''differentials'' and means exactly that: $$ \frac{\partial (aX)}{\partial X} = a $$

answered Dec 15 '17 at 21:06

Emilio Novati

Now I got the twist. Thank you. I originally thought that the denominator (differentiating with..) was omitted only for brevity. Thank you for clarifying – George Pligoropoulos Dec 15 '17 at 21:08

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