MATLAB: Index exceeds Matrix Dimensions

MATLABode45

I'm trying to solve a differential equation using ode45, its working fine with the 2 DOF system but keeps giving "index exceeds matrix dimensions" for a 4 DOF system
function y_dot = ode_sin_roll (t,y)
global A U itv w
y_dot = zeros(4,1);
if t<itv
  y_dot = A*[y(1) ; y(2) ; y(3) ; y(4)] + U*(0.1*(sin(w*t))^2);
else
  y_dot = A*[y(1) ; y(2) ; y(3) ; y(4)];
end
clear all; close all; clc
filename = 'VD_A4_D2.xlsx';
sheet = 1;
range = 'AN4:BC14';
DATA = xlsread(filename, sheet, range);
vx = [1; 5; 10; 15; 20; 25; 30; 35; 40; 45; 50];
for i = (1:length(DATA))
  A11 = DATA(i,1);
  A12 = DATA(i,2);
  A13 = DATA(i,3);
  A14 = DATA(i,4);
  A21 = DATA(i,5);
  A22 = DATA(i,6);
  A23 = DATA(i,7);
  A24 = DATA(i,8);
  A31 = DATA(i,9);
  A32 = DATA(i,10);
  A33 = DATA(i,11);
  A34 = DATA(i,12);
  A41 = DATA(i,13);
  A42 = DATA(i,14);
  A43 = DATA(i,15);
  A44 = DATA(i,16);
  U11 = 353.5;
  U21 = -276.9;
  U31 = 0;
  U41 = 1300.5;
  global A U itv w
  A = [ A11 A12 A13 A14; A21 A22 A23 A24; A31 A32 A33 A34; A41 A42 A43 A44]; %A Matrix of Constants
  U = [ U11 ; U21 ; U31 ; U41 ]; % U Vector of constants
  itv = 100/vx(i,1);
  w = pi*(1/itv);
    [Ts, Ys] = ode45('ode_sin_roll', [0 10], [0 0]);
    plot(Ts, Ys(:,1))
    xlabel('Time (s)')
    ylabel('v_y(m/s)')
    hold on
end
legend1 = legend('1','5','10','15','20','25','30','35','40','45','50');

Best Answer

In your
[Ts, Ys] = ode45('ode_sin_roll', [0 10], [0 0]);
line, the [0 0] is the initial values for the y that will be passed in to your ode function. If you want your y to have 4 elements then you need to pass in something that is 4 elements long instead of [0 0]
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