Function to compute product of all numbers from 1 to n

Hi,

I'm trying to solve the following problem: "Write a Matlab function that recursively computes the product of the integers from 1 to n". My code isnt' working though. This is what I got so far:

function r = integerproduct (n)

b = 1;
vector = 1:n;

for i = 1:length(vector)
    while i <= 5
       q = vector(i)*vector(i+b)
    end
    b=b+1;
    r = q*vector(i+b)
end

end

I just used n = 5 as an example. If I understand the exercise correctly, the function is supposed to compute the following: 1*2*3*4*5 = 120.

It takes forever to run the code which seems a bit dodgy, surely it's not supposed to take that long? Does anyone have any hints as to what I should change so that 1) the function actually does what it's supposed to do and 2) the code runs as efficiently as possible?

Many thanks,

Dobs

Answer 1

[Matt J]

integerproduct(5)

ans = 120

function r = integerproduct (n)

  if n==1, r=1; return; end
  
  r=n*integerproduct(n-1);

end

[Dobs]

Oh yes, it's working now! Thank you! I don't really understand what the function does though. So n == 1 checks if n is equal to 1? And how is the last line able to compute the product? The function is already used inside the function itself?

[Matt J]

The function is already used inside the function itself?

Yes, that's what recursion is.

[Dobs]

Oh, I thought it meant that the function keeps going until n is reached (whatever n is). Thank you for clarifying!