Undefined function or variable (h)

I keep getting undefined function or variable h. This is my code to determine Euler's approximation for N=500 and N=5000

f=inline('2*y','t','y')

y(2)=y(1)+h*f(t(1),y(1)), t(2)=t(1)+h,

y(3)=y(2)+h*f(t(2),y(2)), t(3)=t(2)+h,

y(1)=3; t(1)=0; h = 0.1;

for n = 1:5

y(n+1)= y(n)+h*f(t(n),y(n));

t(n+1) = t(n)+h;

end

[t500,y500] = euler(f,[0,.5],3,500);

[t5000,y5000] = euler(f,[0,.5],3,5000);

t = linspace(0,.5,100); y = 3*exp(2*t); % evaluate the exact solution

plot(t500,y500,'ro-',t5000,y5000,'bx-',t,y,'k-'); axis tight;

legend('Euler N = 500','Euler N = 5000','Exact',2);

This is my function file:

function [t,y] = euler(f,tspan,y0,N)

% Solves the IVP y' = f(t,y), y(t0) = y0 in the time interval tspan = [t0,tf]

% using Euler's method with N time steps.

% Input:% f = name of inline function or function M-file that evaluates the ODE

% (if not an inline function, use: euler(@f,tspan,y0,N))

% For a system, the f must be given as column vector.

% tspan = [t0, tf] where t0 = initial time value and tf = final time value

% y0 = initial value of the dependent variable. If solving a system,

% initial conditions must be given as a vector.

% N = number of steps used.

% Output:

% t = vector of time values where the solution was computed

% y = vector of computed solution values.

m = length(y0);

t0 = tspan(1);

tf = tspan(2);

h = (tf-t0)/N; % evaluate the time step size

t = linspace(t0,tf,N+1); % create the vector of t values

y = zeros(m,N+1); % allocate memory for the output y

y(:,1) = y0'; % set initial condition

for n=1:N

y(:,n+1) = y(:,n) + h*f(t(n),y(:,n)); % implement Euler's method

end

t = t'; y = y'; % change t and y from row to column vectors

end

Answer 1

[John D'Errico]

Well, think about it. Line 2 of your code uses the variable h.

Have you ever defined a variable h before that point? MATLAB cannot read your mind to know what it might be.

When you have a problem like this, execute your code ONE line at a time. Then think about the error it gives you. Look at the variables in that line to see what might the error tell you.