newbie question: howto evaluate functions only once

I think you want an array function:

(%i1) f[a,b] := (print("computing"), a + b);
(%o1) f[a,b]:=(print(computing),a+b)

(%i2) f[3,4];
computing
(%o2) 7

(%i3) f[3,4];
(%o3) 7

For more information, enter: ? functions;

Barton

-----maxima-bounces at math.utexas.edu wrote: -----

>To:?maxima at math.utexas.edu
>From:?andre?maute?<andre.maute at gmx.de>
>Sent?by:?maxima-bounces at math.utexas.edu
>Date:?10/01/2009?04:03PM
>Subject:?[Maxima]?newbie?question:?howto?evaluate?functions?only?once
>
>What?is?the?standard?maxima?way?to?avoid?additional?function?evaluation,
>
>if?the?set?of?the?function?parameters?is?apriori?known?to?be?small?
>
>
>
>For?numbers?I?use?the?following?method
>
>
>
>--------------------------------------------------
>
>~$?maxima?-b?evalonce.max
>
>Maxima?5.19.1?http://maxima.sourceforge.net
>
>Using?Lisp?SBCL?1.0.18.debian
>
>Distributed?under?the?GNU?Public?License.?See?the?file?COPYING.
>
>Dedicated?to?the?memory?of?William?Schelter.
>
>The?function?bug_report()?provides?bug?reporting?information.
>
>(%i1)?????????????????????????batch(evalonce.max)
>
>
>
>batching?/home/user/evalonce.max
>
>(%i2)??????????????????????????display2d?:?false
>
>(%o2)?false
>
>(%i3)?f(x):=block(print("hello"),return(x))
>
>(%i4)?if?not?constantp(h[2])?then?block(h[2]:f(2))
>
>hello
>
>(%o4)?2
>
>(%i5)?if?not?constantp(h[2])?then?block(h[2]:f(2))
>
>(%o5)?false
>
>(%i6)?if?not?constantp(h[3])?then?block(h[3]:f(3))
>
>hello
>
>(%o6)?3
>
>(%i7)?if?not?constantp(h[3])?then?block(h[3]:f(3))
>
>(%o7)?false
>
>(%i8)?arrayinfo(h)
>
>(%o8)?[hashed,1,[2],[3]]
>
>(%i9)?listarray(h)
>
>(%o9)?[2,3]
>
>--------------------------------------------------
>
>
>
>As?one?can?see?"hello"?is?printed?only?two?and?not?four?times.
>
>But?what?should?one?do?if?the?output?of?f?is?more?complicated,
>
>e.g.?expressions?with?sin?and?cos?functions?
>
>
>
>For?me?it?would?be?enough,
>
>if?I?could?decide?if?something?has?already?been?assigned?to?e.g.?h[2].
>
>With?constantp?I?can?do?this?only?for?constants.
>
>
>
>Andre
>
>
>
>
>
>
>
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