Moby wrote:
>
> Raymond Toy wrote:
>> Moby wrote:
>>
>>> I have what is probably a very simple question. I have a function
>>> defined in Maxima, say the following:
>>>
>>> G(s) := 1/(3*s^2+2*s+1)
>>>
>>> Now I would like to define a variable r such that
>>>
>>> r^2 = 3*s^2
>>>
>>> and then define G(s) in terms of this new variable r. How does one go
>>> about achieving this in Maxima?
>>>
>> Perhaps this will help:
>>
>> subst([s = r/sqrt(3)], 1/(3*s^2+2*s+1))
>> -> 1/(r^2+2*r/sqrt(3)+1)
>>
>> Ray
>>
>>
>>
> Many thanks Raymond - is it possible to have Maxima itself work out the
> first paramter, namely the value of s in terms of r?
I kind of purposely didn't have maxima solve for s in terms of r for
your substitution. But you can do it via solve:
soln:solve(r^2=3*s^2,s) ->
[s = -r/sqrt(3), s = r/sqrt(3)]
I assume you want the second solution, so we can do something like
subst(soln[2], 1/(3*s^2+2*s+1))
to get the answer.
There may be better ways....
Ray