Simple ODE solving using ODE45

Question

Mario Méndez 2015-9-8

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/241243-simple-ode-solving-using-ode45

回答： Star Strider 2015-9-8

I am trying to solve a ODE using ODE45, but Matlab keeps give me this message. I really don't understand where is the problem. Error using feval Undefined function 'func' for input arguments of type 'double'.

Error in odearguments (line 87) f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode45 (line 113) [neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn, ...

My code is

function f = func(t)
f = 0.594689181*(1/(0.594689181)^2+(0.298222773)^4/4*(1/t)+(0.127125232)^2+4*(0.357907906)^2*t^2+9*(0.291984971)^2*t^4+16*(0.105174606)^2*t^6-(0.298222773)*(0.127125232)*1/(sqrt(t))-2*(0.298222773)*(0.357907906)*sqrt(t)+3*(0.298222773)*(0.291984971)*t*sqrt(t)-4*(0.298222773)*(0.105174606)*sqrt(t)*t^2+4*(0.127125232)*(0.357907906)*t-6*(0.127125232)*(0.291984971)*t^2+8*(0.127125232)*(0.105174606)*t^3-12*(0.357907906)*(0.291984971)*t^3+16*(0.357907906)*(0.105174606)*t^4-24*(0.291984971)*(0.105174606)*t^5)^0.5;
[xsolv tsolv] = ode45('func',[0.1:0.001:1.02], 0.12523);
end

As simple as that. Thanks in advance!

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Answer 1

Star Strider 2015-9-8

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在 MATLAB Online 中打开

The error I got initially was due to your not having two input arguments in your ODE function. It’s also best to not put your ODE solver call inside your ODE function. This can create recursion problems.

This works for me:

func = @(t,y) 0.594689181*(1/(0.594689181)^2+(0.298222773)^4/4*(1/t)+(0.127125232)^2+4*(0.357907906)^2*t^2+9*(0.291984971)^2*t^4+16*(0.105174606)^2*t^6-(0.298222773)*(0.127125232)*1/(sqrt(t))-2*(0.298222773)*(0.357907906)*sqrt(t)+3*(0.298222773)*(0.291984971)*t*sqrt(t)-4*(0.298222773)*(0.105174606)*sqrt(t)*t^2+4*(0.127125232)*(0.357907906)*t-6*(0.127125232)*(0.291984971)*t^2+8*(0.127125232)*(0.105174606)*t^3-12*(0.357907906)*(0.291984971)*t^3+16*(0.357907906)*(0.105174606)*t^4-24*(0.291984971)*(0.105174606)*t^5)^0.5;
[xsolv, tsolv] = ode45(func,[0.1:0.001:1.02], 0.12523);

I created ‘func’ as an anonymous function, and added the second argument (that must be in the function definition even if you don’t use it).