Unable to solve exercise using duffing equation

The first part were M1=M2=0, I can't introduce the initial values for x1(0=Vector[ 0.1:0.1:2] the code that I used is:

f=@(t,x)[x(2);x(1)-2*x(1)^3];
x1_cond=0.1:0.1:2;
x2_cond=0;
timespan=0:0.001:2;
[t,x]=ode45(f,timespan,[x1_cond;x2_cond]);
plot(t,x)

But there is a error for the initial conditions:

Error using vertcat

Dimensions of arrays being concatenated are not consistent.

Please help me I am new using Matlab

Answer 1

[darova]

Where is blue part?

You should use for loop to calculate for different γ

gamma = 0.1:0.1:2;
for i = 1:length(gamma)
    x1_cond=gamma(i)
    % ...
end

[Maria Cuellar]

The blue part is cancelled because, It says that assume m1=m2=0 so I canceled the terms,