Ode45 problem with equations

Question

buszcini 2019-5-19

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/462935-ode45-problem-with-equations

关闭： MATLAB Answer Bot 2021-8-20

parameters.mat

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I'm having problems with properly typing in four 2nd order differential equations into ode.45 function.

The code looks like this:

load parameters
t0=0:0.01:10;
X01=zeros(8,1);
for k = 1:length(xr)
    [t1,X2] = ode45(@(t,x)f1(t,x,dxr(k),dyr(k),xr(k),yr(k)),t0,X01);
end

And the function

function dX=f1(t,x,dxr,dyr,xr,yr)
m1=10;
mn=10;
p = 1;
R = 0.01;
u = 0.7;
ks = 1.5 * 10^8;
g=9.81;
F1r = ((yr - x(6))^p)*ks*(1 - ((1 - (R^2))/2)*(1 - sign(yr - x(6))*sign(dyr - x(2))));
T1r = -u * F1r * sign(x(1) - dxr);
F21 = ((x(6) - x(8))^p)*ks*(1 - ((1 - R^2)/2)*(1 - sign(x(6) - x(8))*sign(x(2) - x(4))));
T21 = -u * F21 * sign(x(3) - x(1));
M=zeros(8,8);
M(1,1) = m1;
M(2,2) = m1;
M(3,3) = m1;
M(4,4) = m1;
M(5,5) = 1;
M(6,6) = 1;
M(7,7) = 1;
M(8,8) = 1;
dx1=x(1,1);
dy1=x(2,1);
dx2=x(3,1);
dy2=x(4,1);
x1=x(5,1);
y1=x(6,1);
x2=x(7,1);
y2=x(8,1);
Q = [T1r - T21; F1r-m1*g-F21; T21; F21-m1*g; dx1; dy1; dx2; dy2];
dX=inv(M)*Q;
end

It just gets stuck and doesn't execute single loop on ode45.

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John D'Errico 2019-5-19

编辑：John D'Errico 2019-5-19

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I itried looking at your code. The very first thing I would do is to execute your function F1, at the initial values. LOOK AT WHAT IT RETURNS. Does it execute at all? What happens? But that fails of course, because we don't have those other parameters, thus

%dxr, dyr, xr, yr are defined earlier parameters

That makes it impossible to execute your code to test it out.

If you want help, then make it easy for someone to help you.

buszcini 2019-5-19