How do I solve the following second order differential equation?

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John O'Brian
John O'Brian 2017-10-22
评论： John O'Brian 2017-10-26
Can you give me the code on how to solve the following equation?
1.4x'' + 4x' + 1700x = - [-8x' + 20(x')^3 + 100x - 2.5x^3]
Thanks!

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回答（1 个）

Ramanuja Jagannathan
Please find below the documentation link showing how to represent differential equations in MATLAB and solve them. https://www.mathworks.com/help/symbolic/solve-a-single-differential-equation.html
Hope this helps
  2 个评论
John O'Brian
John O'Brian 2017-10-25
编辑：Torsten 2017-10-26
Hi I have the following code:
syms y(t)
[V] = odeToVectorField(1.4*diff(y, 2) == 8*diff(y)-20*(diff(y)).^3-100*y+2.5*y.^3-4*diff(y)-1700*y);
M = matlabFunction(V,'vars', {'t','Y'});
sol = ode45(M,[0 20],[0.01 0]);
opts = odeset('OutputFcn',@odephas2); % Options Structure
tspan = linspace(0, 1, 100); % Times For Evaluation
ic = [0 1]; % Initial Conditions
[t, xt] = ode45(EqnFcn, tspan, ic);
figure(1)
[t, xt] = ode45(EqnFcn, tspan, ic, opts);
title('Phase Plane Plot')
axis equal
figure(2)
plot(t, xt)
grid on
title('Time Domain Plot')
EqnSubc = regexp(sprintf('%s\n',Eqn_subs), '\n','split');
legend(EqnSubc{1:end-1})
I am trying to plot a phase plane plot for a variety of initial conditions. I think it might require a for loop. Can you adjust the code and show me how to do it please?

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