Symbolic differential equation problem

Question

0 个投票

code.txt

*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