MATLAB: 4th Order ODE in Simulink

4th order odeodeode45simulink

I have attached the question I am working on and the previous question (as it pertains to this problem). The previous question asks me to solve a 4thorder ODE in matlab using ode45. I have done this and attached my code below. The question I need help on is how to solve this problem in simulink. I've also attached a pic of my work so far. Thanks for your help

Best Answer

Try the attached model. See if it works for you. Note that the system can not be solved at the time 4.96, therefore I set the end time as 4.5.

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MATLAB: Solving 4th order ode

Use bvp4c()

You already have written your equation as system of first-order equations

function dydt = ode4(t,y)
    L=1;B=0.25;k=0.1;
    dydt = zeros(4,1);
    dydt(1)=y(2);
    dydt(2)=y(3);
    dydt(3)=y(4);
    dydt(4)=(2.*B+1+y(1)).*y(3))./(k.*(1+y(1));
end

Here is function for your boundary conditions

function res = bc4(y0, y1)
    res = [y0(1)-0        % y(0) = 0
           y0(2)-1        % y'(0) = 1
           y1(1)-0        % y(end) = 0
           y1(2)-1];      % y'(end) = 1
end

See bvp4c

MATLAB: 4th degree equations

r = roots([a,b,c,d,e]);
r(imag(r)~=0) = [];  %remove complex
r(r <= 0) = [];  %remove non-positive
min(r)  %now it is the smallest positive real root

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MATLAB: Solving 4th order ode

MATLAB: 4th degree equations

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