Why do some commands run faster and some slower in the command line than in an M.file?
I'm trying to speed up the time it takes my code to run. I looked at the online tutorial and generated a test script using the pre-allocating arrays example from:
If I run the loops with the index of a million (as in the example) it takes to long to run over 30 min; therefore, my test.m file loops are reduced to 100000.
When I run my code I get:
Elapsed time is 29.813208 seconds.
Elapsed time is 0.005239 seconds.
When I execute the same commands from the "command line" I get:
>> clear
>> tic;x = 0;for k = 2:100000;x(k) = x(k-1) + 5;end;toc
Elapsed time is 29.517578 seconds.
>> clear
>> tic;x = zeros(1, 100000);x = 0;for k = 2:100000;x(k) = x(k-1) + 5;end;toc
Elapsed time is 29.077256 seconds.
>>
Notice there is very little difference between in time between the first loop (not pre-allocated) and second loop (pre-allocated). Also it appears that the first loop was a little faster from the command line than from the M file.
M-file code is as follows:{
% Test.m file for checking cpu compute time W/ & w/o preallocating arrays
clear; % clear variables (for testing purposes)
clc; % clears "output" screen
tic %start stopwatch timer
x = 0;
for k = 2:100000
end;
toc %end stopwatch timer
clear; % clear variables (for testing)
tic %start stopwatch timer
x = zeros(1, 100000); % pre-allocate x
for k = 2:100000
end
toc %end stopwatch timer
}
System info: Matlab 7.5.0 (R2007b) XP Home (32 bit) on Mac Book Pro (MBP) Intel Core 2 Duo P8600 @ 2.4Ghz 2GB of ram
