Prev: Loading specific variables from multiple '-mat' files
Next: USB HID interfacing
From: Hueihan on 6 Aug 2010 13:29
Hi, all
I was trying to optimize the speed of my codes and discovered something interesting..

I tried
(1) load a mat file and pass the variables into a function
vs
(2) pass the filename into the function and load mat files inside the function

(1) takes 0.003 sec, almost 30 times faster than (2), which takes
0.086 sec

I guess loading mat file outside v.s. inside a function differ in terms of memory allocation, but why does this affect the speed so much ?
====================================
main.m
====================================

a.x = rand(100,1); b.x = rand(100,1);
filename = 'structure.mat'; save(filename,'a','b');
clear a b

% (1)
tic
load(filename,'a','b');
pass_structure(a,b);
toc

% (2)
tic
pass_matfile(filename);
toc
====================================
pass_structure.m
====================================

function pass_structure(a,b)

tmp = 1024;
for i = 1:length(a.x)
for j = 1:length(b.x)
dist = abs(a.x(i)-b.x(j));
tmp = min(tmp,dist);
end
end
====================================
pass_matfile.m
====================================
function pass_matfile(filename)
load(filename,'a','b');
tmp = 1024;
for i = 1:length(a.x)
for j = 1:length(b.x)
dist = abs(a.x(i)-b.x(j));
tmp = min(tmp,dist);
end
end
From: Matt Fig on 6 Aug 2010 13:57
Try this instead:

S = load(filename,'a','b');
a = S.a;
b = S.b;

I think the parser is slowed by your poofing of variables a and b.
From: Hueihan on 6 Aug 2010 14:28
"Matt Fig" <spamanon(a)yahoo.com> wrote in message <i3hidg$c1f$1(a)fred.mathworks.com>...
> Try this instead:
>
> S = load(filename,'a','b');
> a = S.a;
> b = S.b;
>
> I think the parser is slowed by your poofing of variables a and b.
right..
 | 
Pages: 1
Prev: Loading specific variables from multiple '-mat' files
Next: USB HID interfacing