Issues when stracting from an ODE 45 that depends on a derivative

Question

Mikel 2023-4-21

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1950838-issues-when-stracting-from-an-ode-45-that-depends-on-a-derivative

编辑： Torsten 2023-4-21

Hello,

I'm using ode 45 for some operations but I have a small issue when It comes to extract intermediate variables, it gives me ereor when I try to extract them.

I went into the function and it seems that the variables (dyc,u and ,yc) are filling with empty values as one of the term needs to be derivated inside the function. How can I extract this values?

I'm new to ODEs and Im having some issues using them, sorry!

clear variables;
close all;
clc;
%% INIT
% load("trac.mat","qtraj","dqtraj","ddqtraj")
% solving the ode
t0=0;
tfinal=8;
tspan  = linspace(t0, tfinal, 8e4);
x0     = [1 -2];
[t, x] = ode45(@(t,x) smc_obsv(t,x), tspan, x0);
s = zeros(numel(t),1);
u = s;
yc = s;
% THIS LINE GIVES ME error, I dont know how to solve it
for i = 1:numel(t)
  [~, s(i),u(i),yc(i)] = smc_obsv(t(i), x(i,:));
end
%compute tracking error
y = x(:,1);
e = yc - y;
%% LOOP 
% describing the ode
function [dot,s,u,yc] = smc_obsv(t, x)
    
    % parameters
    f       = sin(2*t); % disturbance
    c       = 1.5;                          %
    r       = 2; 
    % yc, desired track
    yc      = 2*cos(t);
    
    % compute desired velocity and acceleration 
    % THIS VALUE IS EMPTY!!
    dyc     = diff(yc)./diff(t);
    %sliding variable
    s= dyc+c*yc-x(1)*c-x(2);
    %control law U
    u       = - r*tanh(s);
    x1dot = x(2);
    x2dot = f' + u;
    x3dot = x(1);
    dot = [x1dot x2dot x3dot]';
    
end