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How do I fix the "index exceeds matrix dimensions error?

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Cassidy
Cassidy 2016-4-8
关闭： MATLAB Answer Bot 2021-8-20
%Inputs
m = 2000;
I = 3600;
a = 1.3;
b = 1.5;
l = 2.8;
k = 35000;
c = 3800;
v = 20;
A = .10;
L = 1.5*l;
t = 0:0.001:4;
y0 = 0;
dy0 = 0;
theta0 = 0;
dtheta0 = 0;
%ODE Solver
[t,X] = ode45(@DE,t,[y0,dy0,theta0,dtheta0],[],m,I,a,b,l,k,c,v,A,L);
X = transpose(X);
%this is my function DE
function dX = DE(t,m,I,a,b,l,k,c,v,A,X,L)
y1 = (A*sin((2*pi*v*t)/(L)));
y2 = (A*sin((2*pi*(v*t-l))/(L)));
dy1 = (2*pi*v)/(1.5*l)*A*cos((2*pi*v*t)/(L));
dy2 = (2*pi*v)/(1.5*l)*A*cos((2*pi*v*t)/(L));
%it says the error is this next line
dX = [X(2);(k*y1+k*y2+c*dy1+c*dy2-2*c*X(2)-c*(a-b)*X(4)-2*k*X(1)*k*(a-b)*X(3))/m;X(4);(k*a*y1-k*b*y2+c*a*dy1-c*b*dy2-c*(a-b)*X(2)-c*(a^2+b^2)*X(4)-k*(a-b)*X(1)-k*(a^2+b^2)*X(3))/I];
end

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回答（2 个）

Walter Roberson
Walter Roberson 2016-4-8
Change
[t,X] = ode45(@DE,t,[y0,dy0,theta0,dtheta0],[],m,I,a,b,l,k,c,v,A,L);
to
[t,X] = ode45(@(t,X) DE(t,m,I,a,b,l,k,c,v,A,X,L), t, [y0,dy0,theta0,dtheta0]);
  1 个评论
Cassidy
Cassidy 2016-4-8
When I tried that I got this error message,
Warning: Failure at t=2.797947e-01. Unable to meet integration tolerances without reducing the step size below the smallest value allowed (8.881784e-16) at time t. > In ode45 (line 308) In CA2 (line 21)
Mischa Kim
Mischa Kim 2016-4-8
编辑：Mischa Kim 2016-4-8
Cassidy, it is the placement of the state vector in the function call to ode45 and the function
[t,X] = ode45(@DE,t,[y0,dy0,theta0,dtheta0],[],m,I,a,b,l,k,c,v,A,L);
and the function header
function dX = DE(t,X,m,I,a,b,l,k,c,v,A,L)
Put together, try
function DE_test()
m = 2000; I = 3600; a = 1.3; b = 1.5; l = 2.8; k = 35000; c = 3800; v = 20;
A = .10; L = 1.5*l; t = 0:0.001:4; y0 = 0; dy0 = 0; theta0 = 0; dtheta0 = 0;
[t,X] = ode45(@DE,t,[y0,dy0,theta0,dtheta0],[],m,I,a,b,l,k,c,v,A,L);
X = transpose(X);
end
function dX = DE(t,X,m,I,a,b,l,k,c,v,A,L)
y1 = (A*sin((2*pi*v*t)/(L)));
y2 = (A*sin((2*pi*(v*t-l))/(L)));
dy1 = (2*pi*v)/(1.5*l)*A*cos((2*pi*v*t)/(L));
dy2 = (2*pi*v)/(1.5*l)*A*cos((2*pi*v*t)/(L));
dX = [X(2); ...
(k*y1+k*y2+c*dy1+c*dy2-2*c*X(2)-c*(a-b)*X(4)-2*k*X(1)*k*(a-b)*X(3))/m;...
X(4);...
(k*a*y1-k*b*y2+c*a*dy1-c*b*dy2-c*(a-b)*X(2)-c*(a^2+b^2)*X(4)-k*(a-b)*X(1)-k*(a^2+b^2)*X(3))/I];
end

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