How to write a program to solve a difference equation in Matlab?

We want to write a program in MATLAB for the function: p(t+1) = f_alpha(p(t)) = alpha*p(t)*e^(-p(t)), alpha > 0. The program has to plot for a given value of alpha and initial population density p0 the solution p of the function versus time t.

function function(alpha,x)
t=1000;
y=zeros(t,1);
y(1)=x;

if alpha >0
hold on;
for j=2:t;
y(j)=alpha*y(j-1)*exp(-y(j-1));
end
hold off;

n=1:t
plot(n,y);
else
fprintf('alpha has to be positive')
end

or

function function(alpha,n)
if a>0
x=n:0.001:10
f=@x a*x.*exp(-x);

hold on;
plot(x,f(x));
hold off;
xlabel('time');
ylabel('population');
hold off;
else
fprintf('alpha has to be positive.')
end

We don't know which one is better and how we can complete the program.

[John D'Errico]

Um, neither is better. Neither will work. You cannot call a function with the name function. In the second, you use a, but pass in alpha. Lots of other problems.

[Torsten]

The first version looks correct, the second looks wrong to me .

But don't call a function "function". And don't plot inside the function where you compute y, but in the calling program. Make y an output of your "function".

Best wishes

Torsten.