Can ode45 be used to solve mx'' + cx' + kx^1.1=0 x(0)=5;x'(0)=0? Getting complex numbers in answers.

I want to examine the transient response of a second order system with a nonlinear spring force. For example Fspring=kx^n where 0<n<2. I get answers when using ode45, but also a warning, when n is not =1, when plotting that tells that the numbers are complex but only the real part is plotted. Can ode45 be used for this problem? If not, can you suggest alternate. Thanks....version 9.7.0.1296695 (R2019b) Update 4

[Richard Klein]

Thanks for your quick response. The complex answers were bothersome to me, and I have since seen an error in my problem formulation. Your answer helped push my thinking in the right direction. Thanks again.

Answer 1

[Star Strider]

You need to plot the real and complex parts separately.

Assuming:

[t,y] = ode45(yourOdefcn, tspan, ic);

plot it as:

figure
plot(t, real(y))
hold on
plot(t, imag(y))
plot(t, abs(y))
hold off
grid

depending on the result you want.

.

[Star Strider]

As always, my pleasure!