rtoy
commented
2 weeks ago Imported from SourceForge on 2024-07-01 18:08:58 Created by tomasriker on 2017-09-20 06:52:09 Original: https://sourceforge.net/p/maxima/bugs/3333/#534f
If I understand you correctly, you want to move a constant factor out of a differentiation operation. This is not what expand does. expand only expands things like (x+1)*(x-1) to x^2-1 or (x+1)^2 to x^2+2*x+1.
I think the problem is that the constant factor is only moved outside at the time of doing diff(...). In your case, you pass an unknown function q(t) to diff. If Maxima knew at that time that q(t) = C * u(t), it would work. Replacing it afterwards is too late.
So you'll probably want to define a real function like this:
q(t) := C * u(t);
i(t) := diff(q(t), t);i(t) is then correctly C*('diff(u(t),t,1)).
Imported from SourceForge on 2024-07-01 18:08:57 Created by zakhmak on 2017-09-19 19:45:40 Original: https://sourceforge.net/p/maxima/bugs/3333
Hello, I discover a strange behavior regarding expand() command inside wxMaxima. I wrote a ticket on the wxMaxima bug tracking system firstly https://github.com/andrejv/wxmaxima/issues/926 but unfortunately the staff couldn't help me to resolve this singularity. So it was instead recommended to me to contact directly the Maxima staff because wxMaxima a front end for Maxima is.
Concerning the problem, you can find below protocol describing how to reproduce it. I don't know if it Is this really a bug. I tried it not only in wxMaxima but also directly in the Maxima console that informs: Maxima 5.38.1 using Lisp SBCL 1.3.4.
I don't understand what really differs expression e4 from expression e5 except that one expression to expand is saved in a variable. Thanks in advance for any reply
dummy dependency (scale factor) e1: q(t) = C * u(t);
derivation of the quantity e2: i(t) = diff(q(t),t);
replace quantity with its dependencies in the derivation e3: subst(rhs(e1), q(t), e2);
request to move the (constant) scale factor outside the derivation operator as I expected (but that doesn't work) e4: expand(rhs(e3));
only way I succeed to move the (constant) scale factor outside the derivation operator (working but only for this transmitted expression) e5: expand(diff((C*u(t)),t));