MATLAB: Error in simple ode45 functions

MATLABodeode45

Hello, I am trying to solve a non-stiff 2nd order ODE with ode45 function. My ODE is d^2y/dt^2 = -g + (4/15)*(1/m)*(dy/dt)^2

Here is the ode function file that I made

function [ ode_fun_vect ] = ode_1_fun( t,z )
global m g
m=80;
g=9.81;
ode_fun_vec=[z(1);-g+(4/15)*(z(1))^2/m];
end

And here is script to solve ode:

clc;
clear all;
close all;
initial_cond=[600,0];
time_range=[0,20];
[t,y]=ode45(@ode_1_fun,time_range,initial_cond);
figure();
subplot(2,1,1);
plot(t,y(:,1));
xlabel('time');
ylabel('displacement');
subplot(2,1,2);
plot(t,y(:,2));
xlabel('time');
ylabel('velocity');

However I am getting some errors saying: Output argument "ode_fun_vect" (and maybe others) not assigned during call

Can someone help me? Thanks in advance!

Best Answer

Typo!

You defined ‘ode_fun_vect’ as your function output and ‘ode_fun_vec’ as the value it calculates. Change one or the other and your ODE integrates successfully.

Related Solutions

MATLAB: 4th order Runge-Kutta code that can solve for several intial conditions

Here's a version:

% Initial conditions
t0=0;
x0=0:0.2:1;
y0=1:0.2:2;
dt=0.1;
tz=1;
t_range= t0:dt:tz;
X = zeros(numel(x0),numel(t_range));
Y = zeros(numel(y0),numel(t_range));
x_rk=zeros(1,numel(t_range));
y_rk= zeros(1,numel(t_range));
for n = 1:numel(x0)
    x_rk(1)=x0(n);
    y_rk(1)=y0(n);
    for i=1:length(t_range)-1
        [x_rk(i+1), y_rk(i+1)]=rk_method(x_rk(i),y_rk(i),dt);
    end
    X(n,:) = x_rk;
    Y(n,:) = y_rk;
    %% PLots
    subplot(numel(x0)/2,2,n)
    plot (t_range, x_rk,'b-o',t_range, y_rk,'y-o','MarkerSize',5);
    grid
    title([num2str(x0(n)),'   ',num2str(y0(n))])
    legend('x','y')
end
disp('X = '), disp(X)
disp('Y = '), disp(Y)
%% Functions
function [dxdt, dydt]= f(x,y)
dxdt =  5*x-3*y;
dydt = -6*x+2*y;
end 
function [x1, y1]=rk_method(x0,y0,dt)
[k11, k12]=f(x0,y0);     
[k21, k22]=f(x0+0.5*dt*k11,y0+0.5*dt*k12); 
[k31, k32]=f(x0+0.5*dt*k21,y0+0.5*dt*k22); 
[k41, k42]=f(x0+dt*k31, y0+dt*k32); 
x1=x0+dt*((k11/6)+((k21+k31)/3)+(k41/6));
y1=y0+dt*((k12/6)+((k22+k32)/3)+(k42/6));
end

MATLAB: Error using ode45() to solve a couple of ODE’s

dxdt=[G1.*(N0-a1.*X(1)-a2.*X(2)).*X(1)-k1.*X(1);...
                                         %      ^------ should be a semicolon instead of a comma
    G2.*(N0-a1.*X(1)-a2.*X(2)).*X(2)-k2.*X(2)];

%start position = (0,1)
ODE45_1_Ti=0;
ODE45_1_Tf=10;
ODE45_1_start=[1 1];
[ODE45_1_T,ODE45_1_X]=ode45(@ODE_Set,[ODE45_1_Ti ODE45_1_Tf],ODE45_1_start); %function call
plot(ODE45_1_T,ODE45_1_X)  
 
function dxdt = ODE_Set(t,X)  %function definition
N0=25;
G1=1;G2=1;
a1=6;a2=3;
k1=1;k2=4;
dxdt=[G1.*(N0-a1.*X(1)-a2.*X(2)).*X(1)-k1.*X(1);...
    G2.*(N0-a1.*X(1)-a2.*X(2)).*X(2)-k2.*X(2)];
end

Best Answer

Related Solutions

MATLAB: 4th order Runge-Kutta code that can solve for several intial conditions

MATLAB: Error using ode45() to solve a couple of ODE’s

Related Question