I'm trying to solve two separate systems using ODE23 while controlling the number of indexes so that the indexes are equal for both systems, but I couldn't. Can you help? Than

function [sol1,sol2] = two_system

clc

close all

clear all

opt = odeset('RelTol',1e-3);

sol1 = ode23(@system1,[0 5],[0],opt);

sol2 = ode23(@system2,[0 5],[0],opt);

figure(1)

plot(sol1.x(1,:),sol1.y(1,:),'b','LineWidth',1.5)

hold on

plot(sol2.x(1,:),sol2.y(1,:),'--r','LineWidth',1.5)

L1=length(sol1.x(1,:))

L2=length(sol2.x(1,:))

end

function dydt = system1(t,y)

M1 = y(1);

F_M1= 2;

theta1=0*pi/180;

A1 = 0.01;

%%%%%%% equation_system1 %%%%%%%

dMdt=(A1*(2*pi*(F_M1))*cos(2*pi*(F_M1)*(t)+theta1));

dydt = [dMdt];

end

function dydt = system2(t,y)

M2 = y(1);

F_M2= 2;

theta2=90*pi/180;

A2 = 0.01;

%%%%%%% equation_system2 %%%%%%%

dMdt=(A2*(2*pi*(F_M2))*cos(2*pi*(F_M2)*(t)+theta2));

dydt = [dMdt];

end

[Torsten]

Why don't you solve both equations simultaneously in one call to ode23 ?

Answer 1

[Sam Chak]

Hi @mohammed

Please review if this approach is accceptable.

tspan    = linspace(0, 5, 251);
opt      = odeset('RelTol',1e-3);
[x1, y1] = ode23(@system1, tspan, [0], opt);
[x2, y2] = ode23(@system2, tspan, [0], opt);

figure(1)
plot(x1, y1(:,1),   'b','LineWidth',1.5)
hold on
plot(x2, y2(:,1), '--r','LineWidth',1.5)

L1  = length(x1)

L1 = 251

L2  = length(x2)

L2 = 251

function dydt = system1(t,y)   
    M1 = y(1);
    F_M1= 2;
    theta1=0*pi/180;
    A1 = 0.01; 
    %%%%%%% equation_system1  %%%%%%%
    dMdt=(A1*(2*pi*(F_M1))*cos(2*pi*(F_M1)*(t)+theta1));
    dydt = [dMdt];
end

function dydt = system2(t,y)
    M2 = y(1);
    F_M2= 2;
    theta2=90*pi/180;
    A2 = 0.01; 
    %%%%%%% equation_system2  %%%%%%%
    dMdt=(A2*(2*pi*(F_M2))*cos(2*pi*(F_M2)*(t)+theta2));
    dydt = [dMdt];
end