# [Maxima] Arguments of operatorp

Jérome Laurens jerome.laurens at u-bourgogne.fr
Thu Jun 21 02:07:33 CDT 2012

```Le 20 juin 2012 à 17:21, Robert Dodier a écrit :

> On 2012-06-20, Jérome Laurens <jerome.laurens at u-bourgogne.fr> wrote:
>
>> in the meanwhile, I found one way to walk an expression tree
>> but it was not as convincing as your suggestions.
>> Being new to maxima language and lisp,
>> I must change some of my habits ;-)
>
>> For the short story, my goal is to compute solutions of some systems
>> of partial differential equations in the sense of distributions. No
>> Laplace transform allowed.
>
> Sorry, I wasn't clear. Let me try again.
>
> There are Maxima functions to walk an expression tree and perform some
> operation on designated terms. What is the operation you are trying to
> carry out?

- Fubini
- integration by parts on unbounded domains
- change of variables in 2D
for the soft side, and for the hard side
Given an expression of the form
integrate(f*g,...)
change g according to f and the integral bounds.

Of course, this must apply to subexpressions of bigger ones.
The initial mathematical problem may evolve to better fit maxima commands.
One of the concrete question I came to was

With subst variants we can make a substitution only occur in one specific argument,
for example only in the lower bound of an integrate command.
But is there a tool to find the number arguments of substpart based on general criteria,
for example "the lower bounds of the integrals subexpression in variable 't'"

While reading the doc, I may have missed some kind of find command...

Thanks

--Jérôme

```