dsolve error (simultaneous differential equations)

Question

Seungwon Lee 2020-5-18

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/526418-dsolve-error-simultaneous-differential-equations

评论： Seungwon Lee 2020-5-18

clear all
close
clc
m = 10;
k = 1000;
u0 = 0.01;
syms y1 y2
f=dsolve('m*D2y1+2*k*y1-k*y2==0,m*D2y2-k*y1+2k*y2==0','y1(0)==0,Dy1(0)==0,Dy2(0)==0,y2(0)==0.01');
figure
ezplot(f,[0 100]);

I want to solve simultaneous differential equation but i have a problem solving it.

Can someone help me find whats causing error?

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Answer 1

Sulaymon Eshkabilov 2020-5-18

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/526418-dsolve-error-simultaneous-differential-equations#answer_433201

在 MATLAB Online 中打开

Here is the answer:

clear all
close
clc
m = 10;
k = 1000;
u0 = 0.01;
syms y1(t) y2(t)
Dy1=diff(y1);
Dy2=diff(y2);
D2y1=diff(y1, 2);
D2y2=diff(y2, 2);
Eqn1=m*D2y1+2*k*y1-k*y2;
Eqn2=m*D2y2-k*y1+2*k*y2;
ICs=[y1(0)==0,Dy1(0)==0,Dy2(0)==0,y2(0)==0.01];
f=dsolve(Eqn1,Eqn2, ICs);
figure
ezplot(f.y1,[0 100]), hold on
ezplot(f.y2, [0, 100]), legend('y_1(t)', 'y_2(t)', 'location', 'best')

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Sulaymon Eshkabilov 2020-5-18

There two different ways of expressing ODE expressions. This is one of them and is the logically structured one. The other one is direct that you define your variable without specifying to differentuiate it w.r.t what variable that may create a problem in cases when there is an obscurity with the existing variables in your MATLAB workspace.

Good luck

Seungwon Lee 2020-5-18