MATLAB: Timing multiple Matlab functions

factorial timing

Hi!
I have two different ways of calculating a factorial of any number, for this program its 150!. I want to time the two functions and compare how much time they require in a plot.
This is my code so far:
 clear all, close all, clc
 n=150;
t1=zeros(1,n);
t2=zeros(1,n);
A=zeros(1,n);
B=ones(1,n);
f=1;
 tic;
 for i=1:n
    f=f*i;
    A(1,i)=f;
    t1(i)=toc;
 end;
 tic;
 for i=2:n
  B(i)=B(i-1)*i;
  t2(i)=toc;
end;
 plot(t1,A,t2,B)
I do get a plot with the correct graphs, however I am concerned that the times are not correct since first of all, the first for-loop is faster than the second one and I think it should be around. Also, I have tried changing their places in the program and I get different results when I do.
How can I change this to get Matlab to time these functions accurately? Also, if you have a suggestion I would be very thankful if you could also point out what I am doing wrong.
Thank you!

Best Answer

Hi,
timing single calls within a program using tic/toc won't work, the resolution will simply be too coarse.
What are you trying to find out? If the second or the first is preferable? Why then not simply run the loop and do the timing after the loop.
Additional suggestions: put your code into a function, it will be more realistic and give better results than scripts.
You might put the loops into individual sub functions and call them with different values of n if you are interested in the dependency on n.
Titus
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