Making a function definition where the right hand side is evaluated before the definition is saved

Asked Feb 28 '19 at 22:17

Active Mar 01 '19 at 09:23

Viewed 152 times

My question is about assigning the resulting expression after evaluation of a function.

So what I want:

FOCf[x, y] := D[f[x, y], x]

such it immediately evaluates the right hand side, making it a conditional expression.

How I do it now.

I first shift-enter: D[f[x, y], x]. Then, I manually copy the resulting output to the right end of FOCf[x, y] :=.

Is there a better way to do this? I already tried using Evaluate, but that did not seem to work.

edited Mar 01 '19 at 09:23

asked Feb 28 '19 at 22:17

Dick Oosthuizen

Is f defined prior to defining FOCf? – Edmund Feb 28 '19 at 22:20
4

Not sure how to interpret your question. You can evaluate in place with [Ctrl] + [Shift] + [Enter], or you can use = (without the colon) to first evaluate the r.h.s. and then assign the result to the l.h.s. symbol. Btw., normally you indicate variables with an underscore on the left side, e.g. FOCf[x_, y_]. – JEM_Mosig Feb 28 '19 at 22:23
Yes,f[x_, y_] := "conditional expression" before. I can also plot that one, so that seems fine. – Dick Oosthuizen Feb 28 '19 at 22:24
Thank you, I didn't know about the = . – Dick Oosthuizen Feb 28 '19 at 22:28
1

or you can write FOCf[x, y] := Evaluate @ D[f[x, y], x] – m_goldberg Mar 01 '19 at 07:07
@DickOosthuizen Welcome to Mathematica.SE! I suggest that you take a look on this topic about basic pitfalls in Mathematica. – Pinti Mar 01 '19 at 09:04
Why is this off-topic? Nothing in the the "basic pitfalls" is relevant, and the solution here helped me (= fails when parameter patterns are involved) - although /nothing here explains at all why Evaluate gets treated differently than D with respect to order of evaluation/! – BadZen Mar 20 '22 at 18:28

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