# Using ODE45 for first order diff equation with three different variables

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PetronasAMG on 13 Sep 2021
Edited: darova on 14 Sep 2021
So, I am trying to use ODE45,
say dx/dt = (0.1*x)+(0.25*y)-(9.8*z)
I am trying to graph the behavior of x,y and z from time (0 to 100). What should i do to set up as in funciton file?
i tried
function dxdt = func(t,x,y,z)
dxdt = (0.1*x)+(0.25*y)-(g*z);
end
%main script
tspan = [0 100];
xint = 0;
yint = 0;
zint = 0;
[t,x,y,z] = ode45(func,tspan,xint,yint,zint);
But after i run this code i am getting an error says not enough input arguments.I am still adpoting the concept of using ode function but Please help!
I need to plot x,y,z from 0 to 100
Wan Ji on 14 Sep 2021
Hi, you should have three equations for solving ode of x,y,z with respect to t. But you only provided one

Wan Ji on 14 Sep 2021
For example
function dxdt = func(t,x,g)
dxdt = zeros(3,1);
dxdt(1) = (0.1*x(1))+(0.25*x(2))-(g*x(3));
dxdt(2) = (0.1*x(1))+(0.25*x(2))-(g*x(3));
dxdt(3) = (0.1*x(1))+(0.25*x(2))-(g*x(3));
end
The main function
tspan = [0 100];
g = 10;
[t,x] = ode45(@(t,x)func(t,x,g),[0,100],[0;0;0]);
xsol = x(:,1);
ysol = x(:,2);
zsol = z(:,3);

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