I fixed my typo in the comment above. I had compared /2 and *.5 in my timings and saw little difference. But I see some difference with your first set of numbers (but much smaller than the 30% you are seeing). Thanks for the interesting test cases.

There are obvious ways to vectorize some codes like these, but you can’t always do so.

–Loren

clc
clear all;
N = 1;
M = magic(2000);
K = zeros(size(M));
t = cputime;
for num = 1:N,
K = M*.272423;
end
cputime-t
t = cputime;
for num = 1:N,
K = M/3.67076;
end
cputime-t

on mine it shows 30% better performance for * , however it is really dependant on the case you are solving. sometimes I see 300% improvement.

for the a==1 case I wrote this

clc;
clear all;

t=cputime;

for i=1:20000000
for j=i:5
if 2==j
alpha=200;
end
end
end
cputime-t

clear all;
t=cputime;
for i=1:20000000
for j=i:5
if j==2
alpha=200;
end
end
end
cputime-t

the difference was just 2 sec in 15 sec, but at least showed that the 1==a case was faster

have a good week

I don’t know which version of MATLAB you are using or how you are doing your timing. I used R2006a and ran this script:

N = 1;
M = magic(2000);
K = zeros(size(M));
t = cputime;
for num = 1:N,
    K = M*0.5;
end
cputime-t
t = cputime;
for num = 1:N,
    K = M/2.0;
end
cputime-t

and I basically see no difference in scalar multiplication vs. division.

I similarly tried timing 1==a vs. a==1 and found no difference. I am using a Windows XP laptop.

the first is most of the times it improves the speed dramatically if you use * instead of / if the Denominator is a constant for example instead of a/2 most of the times it helps if you use a*.5 (it makes sense but most of the times we forget to use it)

And one myth is it is better to write your if statements like this ‘if 1==a’ instead of ‘if a==1′ however I still don’t know if it is just a myth or not

And probably everyone knows how to use && ;)

Regular colon notation in for loops fits into the paren behavior.

–Loren

for k=1:theEnd

fit? Is it square or paren?

- Steve

–Loren