Extracting an intermediate vector from ode45

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Mikel
Mikel 2023-4-19
评论： Mikel 2023-4-21
Hello,
I have done search in the forum and found how to exract a variable from a ODE45 function. I'm trying to do the same, though, I'm not able to do it. I need some help on this. s, u and z variables they are suposed to be arrays but I dont know why I can only extract a single value from them. How can I take the whole array from them?
close all;
clc;
%% CONTEXT
% create an observer that estimates x2 while sliding variable and x1,x2
% tends to 0
% x1'=x2 x1(0)=x10
% x2'= u + f(x1,x2,t) x2(0)=x20
% y = x1
% injection term (sliding mode observer)
% v = x1' = x2 = -r1*sign(z1)
% auxiliar sliding variable is the error estimation
% z1= x1s - x1
%% INIT
t0=0;
tfinal= 8;
% solving the ode
tspan = linspace(t0, tfinal, 8e4);
x0 = [1 -2 0 0];
[t, x] = ode45(@(t,x) smc_obsv(t,x), tspan, x0);
%
[~, s,u,z] = smc_obsv(t, x);
%% plotting the solution
figure()
plot(t,x(:,3),'k', 'LineWidth',2)
set(gca,'FontSize',12)
hold on
plot(t,x(:,4),'r', 'LineWidth',2)
grid on
title("speed stimation")
xlabel('time(s)','fontweight','bold','FontSize',12)
ylabel('x2 and x2s ','fontweight','bold','FontSize',12)
legend('x2','x2s')
minPlot = min(x(:,4));
maxPlot = max(x(:,4));
ylim([minPlot, maxPlot]);
figure()
plot(t,s,'k', 'LineWidth',2)
set(gca,'FontSize',12)
grid on
title("Sliding variable")
xlabel('time(s)','fontweight','bold','FontSize',12)
ylabel('s','fontweight','bold','FontSize',12)
legend('sigma')
minPlot = min(sp);
maxPlot = max(sp);
ylim([minPlot, maxPlot]);
figure()
plot(t,x1(1:end-1),'k', 'LineWidth',2)
hold on
plot(t,x2s(1:end-1),'r', 'LineWidth',2)
set(gca,'FontSize',12)
grid on
title("x1 and x2 trough time")
xlabel('x1 and x2s','fontweight','bold','FontSize',12)
ylabel('t','fontweight','bold','FontSize',12)
legend('x1','x2')
xlim([0 8])
%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% describing the ode
function [xdot,s,u,z] = smc_obsv(t, x)
xdot = zeros(4, length(t));
% parameters
f = sin(2*t); % disturbance
c = 1.5; %
r = 2; % criterion: r > max(f)
s = c*x(1) + x(4); % sliding surface
u = - r*tanh(s/0.001) - c*x(4); % control input
r1 = 10; % high gain
z = x(3) - x(1); % estimation error
v1 = - r1*tanh(z/0.001); % rate of xhat_1
LPF = 1/0.01; % adapatation rate
v2 = (v1 - x(4))*LPF; % rate of xhat_2
xdot(1) = x(2);
xdot(2) = f + u;
xdot(3) = v1;
xdot(4) = v2;
end

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采纳的回答

Torsten
Torsten 2023-4-19
Use
s = zeros(numel(t),1);
u = s;
z = s;
for i = 1:numel(t)
[~, s(i),u(i),z(i)] = smc_obsv(t(i), x(i,:));
end
instead of
[~, s,u,z] = smc_obsv(t, x);

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