# [Maxima] confusing solution set of exp-equation

Richard Fateman fateman at cs.berkeley.edu
Mon Apr 16 14:00:22 CDT 2007

```You can often do this:

fun(x):=''f

fun(4)

Maybe that will solve your problem.

It is possible to set derivabbrev:true

to change the output of derivatives to look like subscripts.
If you wish, you might be able to use

df[n]:= diff(f,x,n)

and then a DE might look like    df[2]-a*f=0

RJF

Wolfgang Lindner wrote:

>"Stavros Macrakis" <macrakis at alum.mit.edu> schrieb:
>On 4/15/07, Wolfgang Lindner <LindnerW at t-online.de> wrote:
>
>
>>>(%i1) f(x):=exp(x)-1/4*x*exp(x);
>>>(%i2) solve(f(x)=0,x);
>>>(%o2) [x=4,%e^x=0]
>>>(%i3) diff(f(x),x) ;  /* f prime */ ...
>>>AFAIK it is not possible to abbrevitae  diff(f(x),x)  with  f'(x).
>>>I use fp(x) to name 'f prime' etc.
>>>Is there any symbol left (backquote?) to name f'(x) and causing no problems later?
>>>What is your recommended work around?
>>>
>>>
>
>
>
>>As a general rule, Maxima does a much better job with mathematical *expressions* than
>>with mathematical *functions* with names (like f).
>>So the natural way to handle this sort of thing in Maxima is
>>f: exp(x)-1/4*x*exp(x);
>>solve(f,x)\$
>>solve(diff(f,x),x)
>>etc.>>
>>
>>
>
>Thank you for your interesting hints on Maxima's capabilities. In Germany we have a
>'didactical tradition in math' to perfer *functions* (at least since Felix Klein), not
>terms - but using CAS the situation seems be on other one.
>My students will (fequently) have to calculate function values, function tables etc.
>So - as far as I know - I should have to write
>
>(%i4) subst(x=4, f)  /* instead of f(4) */
>
>if f is an term. Or is there an better possibility?
>If there would be an 'term evaluator' like
>
>(%i4') f | x=4         /* term f evaluated for x =4 */
>
>one would have a simpler and shorter 'functionlike' notation.
>
>So I have to decide: function - maybe no good job
>                     term     - no usual evaluation a la f(x)
>
>
>HTH
>Wolfgang
>Leichlingen/Germany
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>
>
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