Message Boards

WOLFRAM COMMUNITY

6297 Views

1 Reply

1 Total Likes

View groups...

Follow this post

Share this post:

GROUPS:

Mathematics Mathematica Symbolic Computations

Difference between f1[a_, b_] := a[b]^2 and f2[a_][b_] := a[b]^2 etc.

Tomáš Hruš

Posted 11 years ago

Colleagues, please - it is a difference betwen theese defintifions? It seems to me, that tey are equivalent -- it is true? In[1]:= f1[a_, b_] := a[b]a[2 b] In[2]:= f2[a_][b_] := a[b]a[2 b] In[3]:= f3[a_[b_]] := a[b]*a[2 b] In[4]:= {f1[Func, x], f2[Func][x], f3[Func[x]]} Out[4]= {Func[x] Func[2 x], Func[x] Func[2 x], Func[x] Func[2 x]} Can you give me a link for study this theme? Thanks!

Colleagues, please - it is a difference betwen theese defintifions? It seems to me, that tey are equivalent -- it is true?

In[1]:= f1[a_, b_] := a[b]*a[2 b]

In[2]:= f2[a_][b_] := a[b]*a[2 b]

In[3]:= f3[a_[b_]] := a[b]*a[2 b]

In[4]:= {f1[Func, x], f2[Func][x], f3[Func[x]]}

Out[4]= {Func[x] Func[2 x], Func[x] Func[2 x], Func[x] Func[2 x]}

Can you give me a link for study this theme? Thanks!

POSTED BY: Tomáš Hruš

1 Reply

Sort By:

Szabolcs Horvát

Posted 11 years ago

The first two accomplish the very same thing, for as long as you keep them in this form. The third one won't always behave the same way though. Consider fun[x_] := x^2 f3[a_[b_]] := a[b]a[2 b] Then `f3[fun[z]]` will evaluate to `f3[z^2]` because `fun[z]` evaluates first. However, if you set `SetAttributes[f3, HoldAll]`, then it will behave more similarly to `f1` and `f2`: `f3[fun[z]]` will now first evaluate to `fun[z]fun[2 z]`, then to `4 z^4`. This is not the complete story, but giving full details is not always educational. So instead I'll leave you with this reference, which (I think) discusses all the relevant issues: http://reference.wolfram.com/mathematica/tutorial/EvaluationOfExpressionsOverview.html In particular, look at the section on Nonstandard Evaluation and the `Hold...` attributes.

POSTED BY: Szabolcs Horvát

Reply to this discussion

Reply Preview

Attachments

Remove Add a file to this post

Follow this discussion

or Discard

Group Abstract

Feedback