Use function with symbolic variable within ODE45 in van der pol oscillator problem

Question

Aninda pal 2022-10-15

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1827288-use-function-with-symbolic-variable-within-ode45-in-van-der-pol-oscillator-problem

回答： Gokul Nath S J 2022-10-21

I want to call the second order derivative term as a symbolic function insead of the procedure stated in MATLAB documentation. How can I make this run. Thanks in advance.

%%
clear all
clc
syms t y
[t,y] = ode45(@(t,y)vdp1(t,y),[0 20],[2; 0])
function dydt = vdp1(t,y)
syms p1 p2 
EQ1=2*(1-p1^2)*p2-p1;
% dydt = [y(2); 1*(1-y(1)^2)*y(2)-y(1)];
    function k= makfun(EQ1,y(1),y(2))
Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters.
        k=subs(EQ1,[p1 p2],[y(1) y(2)]);
    end
dydt = [y(2); makfun(EQ1,y(1),y(2))];
end

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Gokul Nath S J 2022-10-21

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1827288-use-function-with-symbolic-variable-within-ode45-in-van-der-pol-oscillator-problem#answer_1080448

在 MATLAB Online 中打开

Dear Aninda Pal,

There are few ways by which you can use symbolic to find the derivative. Refer to the code below.

syms  y(t) dydt(t)
y(t) = t^2 + 2*t + 5;
dydt(t) = diff(y(t));

A sample function of y(t) has been created for the demonstration. If you want to evaluate the derivative at a specific point, say 5, just call dydt(5).

Refer to the attached documentation for more info.

Create symbolic scalar variables and functions, and matrix variables and functions - MATLAB syms (mathworks.com)