i have an error at line 13 xi1 and below it. how to correct it for runge kutta method

Question

Alec Jake Cortina 2021-11-25

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1595689-i-have-an-error-at-line-13-xi1-and-below-it-how-to-correct-it-for-runge-kutta-method

回答： Neelanshu 2024-5-10

function [y1] = RK21(x0, y0, h, f)
%RK21.m apply one step of the explicit RK2 method
% with Butcher Tableau: 
% 0
% 2/3 2/3
%     1/4   3/4
%
% xi1 = yk
% xi2 = yk + a21*h*f(xk + c1*h, xi1)
% yk+1 = yk + h( b1*f(xk+c1*h, xi1 ) + b2*f(xk+c2*h, xi2)
xi1 = 0;
xi2 = y0 + 2/3*h*f(x1/4+1/4*h, xi3/4); 
y1 = y0 + h*( 1/4*f(x1/4+1/4*h, xi3/4) + 3/4*f(x1/4+2/3*h, xi2 ));

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Jan 2021-11-25

If you mention an error in the forum, add a copy of the complete message also. It is much easier to solve a problem than to guess, what the problem is.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Neelanshu 2024-5-10

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1595689-i-have-an-error-at-line-13-xi1-and-below-it-how-to-correct-it-for-runge-kutta-method#answer_1455506

Hi Alec,

As Jan mentioned, kindly describe the error you encountered. I assume that the error is Unrecognized function or variable because the equations for computating xi2 and y1 utilize xi3, which hasn't been defined in the function workspace.You'll need to define xi3 before you can compute xi2 and y1 within the function.

Hope this helps.