Symbolic differential equation problem

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Andrew Bobylkov
Andrew Bobylkov 2020-5-28
编辑： Andrew Bobylkov 2020-5-28
*upd: all code attached
I`m trying to input function F(z) into diff.equation with substitution
but after that dsolve doesn`t identify my equation as differential
% F was calculated in upper section of code
% F = F(z) and it will change, so it`s impossible to write it "by hand"
eq = m * diff(z,t,2) - C * (z-z0) == - F;
dsolve(eq)%crash
what`s the problem can be?
F = (39*((130430*z*exp(-3/20))/3 - (130430*z)/3 + 1)^2)/(160*(z(t) - 3/2)^2) - (39*((130430*z)/3 - (130430*z*exp(-3/20))/3 + 1)^2)/(160*(z(t) + 3/2)^2)
p.s. then i need to build phase portrait, if you know good ways to do it, please tell me

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采纳的回答

darova
darova 2020-5-28
The problem is in z_c variable
z_c =
z - z*exp(-t/r)
z(t) should be instead of z
try to change this line
z_c = subs(z_c,[r 'z'],[T1 z])

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