# I am using euler's method to solve a differential equation, but when I run the code it doesn't plot.

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Rashmika Undu on 13 Jan 2022
Commented: James Tursa on 13 Jan 2022
Hi, I am using Euler's method to solve the differential equation dv/dt, but when I run the code it doesn't plot andI don't get an error.
Any help would be greatly appreciated. Thanks
%Eulers method
t0=0; %start time
t1= 500; %finish time
dt = 100000; %large timestep to avoid errors
n = (t1-t0)/dt +1; %Number of nodes
t = linspace(t0,t1,n);%Time array
n_rou = round(n); %rounds n to an integer for y_euler to work
v_euler = zeros(n_rou,1); %create an empty array
v_euler(1) = 1; %initial value as v(0)=1
dvdt = @(v,t) -2.4*v(t)^2 - v(t)^3-4*v(t)+7.4 ; %anonymous function for dv/dt
for i = 1:n-1
f = dvdt(v_euler(i),t(i)); %Evaluate f=dy/dt at i
v_euler(i+1) = v_euler(i) + dt*f; % Evaluate y at i+1
end
plot(t,v_euler)

James Tursa on 13 Jan 2022
Take a look at these lines:
t0=0; %start time
t1= 500; %finish time
dt = 100000;
Your stepsize is much larger than the total time! You need to make the stepsize reasonably small given the total time and derivative function involved.
James Tursa on 13 Jan 2022
Assuming v(t) is meant to be "velocity at time t", you should just drop the (t) part since what is passed in for v is at the current time:
dvdt = @(v,t) -2.4*v^2 - v^3-4*v+7.4