# I am getting error not enough input arguments.

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Puja on 22 Jan 2024
Commented: Sam Chak on 14 Jun 2024
function fval=massSpringFun(t,y)
%Function for mass-spring system
%Define constants
m=1;
c=0.001;
k=100;
h=0.01;
x1=0.01;
x2=0;
%This set of ODEs will be solved using ode45
x1=y(1);
v1=y(2);
x2=y(3);
v2=y(4);
%Definr dy/dt
fval(1,1)=v;
fval(2,1)=(k/m)*(x1-x2)-(c/h)*v2;
%To run the mass spring system
y0=[1;0];
tspan=[0 10];
[tsol,ysol]=ode45(@(t,y)massSpringFun(t,y),tspan,y0);
plot(tsol,ysol(:,1));

Abhimenyu on 14 Jun 2024
Hi Puja,
The issue you are facing is because of the function definition and the initial conditions provided. The 'y0' variable is defined as [1; 0], but the system has four variables (displacements and velocities for two masses). You need to provide initial conditions for all four variables.
Please follow the below-mentioned example MATLAB code to correctly simulate the mass-spring system:
% Define the mass-spring system function
function fval = massSpringFun(t, y)
% Extract variables
x1 = y(1);
v1 = y(2);
x2 = y(3);
v2 = y(4);
% Define constants
m = 1;
c = 0.001;
k = 100;
h = 0.01;
% Define dy/dt
fval(1, 1) = v1;
fval(2, 1) = (k/m) * (x1 - x2) - (c/h) * v2;
fval(3, 1) = v2;
fval(4, 1) = 0; % Assuming no external force on the second mass
end
Providing initial conditions for all the four variables:
% Initial conditions for all four variables
y0 = [1; 0; 0; 0];
% Time span
tspan = [0, 10];
% Solve the ODE system
[tsol, ysol] = ode45(@massSpringFun, tspan, y0);
% Plot the displacement of the first mass
plot(tsol, ysol(:, 1));
xlabel('Time');
ylabel('Displacement (x1)');
title('Mass-Spring System');
grid on;
I hope this helps to solve your query!
Sam Chak on 14 Jun 2024
For a typical mass-spring system, the system should be realistically stable when all energy dissipation mechanisms are accounted for. I have selected some numerical parameter values in order to bring the displacement response back down to a physically realizable range.
function fval = massSpringFun(t, y)
% Extract variables
x1 = y(1);
v1 = y(2);
x2 = y(3);
v2 = y(4);
% Define constants
m = 1;
c = 0.001;
k = 100;
h = 0.01;
% Define dy/dt
fval(1, 1) = v1;
fval(2, 1) = (k/m) * (x1 - x2) - (c/h) * v2;
fval(3, 1) = v2;
fval(4, 1) = 243.39*x1 + 24.36*v1 - 242*x2 - 22.13*v2;
end
tspan = [0, 10];
y0 = [1; 0; 0; 0];
[t, y] = ode45(@massSpringFun, tspan, y0);
plot(t, y(:, 1)), grid on
xlabel('Time'), ylabel('x_{1} Displacement (m)'), title('Mass-Spring System');