Speed Optimization on Fix Matrix Looping

[lain.ux]

Hi,

I have tried to run my octave code with following two test cases and 
gotten the elapsed time. As the result, test case 2 is executed much 
faster than case 1.

Case 1:
b = [];
for i = 1:N
        b(i, 1:P) = i * ones (1, P);
endfor

Case 2:
b = 1.0 * ones (N, P);  # this line doesn't effect the final matrix b
                        # value. but with this line, the execution time
                        # becomes much-much faster
for i = 1:N
        b(i, 1:P) = i * ones (1, P);
endfor

My platform:
 - Processor: Intel Core 2 Duo
 - Operating System: Debian GNU/Linux 4
 - Octave Version: 3.0.1

My questions are:
1) Is the test result correct?
2) Has anyone test about it?

Suggestion:
I see that b = []; is mostly used on Octave codes. If the result is 
correct (can improve the speed), I think, it better to be changed 
automatically during the parsing step so needless for user to change the 
line manually.

Please find the complete test code and result from my blog:
http://l411v.blogspot.com/2008/04/octave-speed-optimization-080426.html

Thanks,
lain.ux