CODEWITHSUNDEEP
performancematlab
Blue7
Blue7

Reputation: 2044

How to reduce time taken for large calculations in MATLAB

When using the desktop PC's in my university (Which have 4Gb of ram), calculations in Matlab are fairly speedy, but on my laptop (Which also has 4Gb of ram), the exact same calculations take ages. My laptop is much more modern so I assume it also has a similar clock speed to the desktops.

For example, I have written a program that calculates the solid angle subtended by 50 disks at 500 points. On the desktop PC's this calculation takes about 15 seconds, on my laptop it takes about 5 minutes.

Is there a way to reduce the time taken to perform these calculations? e.g, can I allocate more ram to MATLAB, or can I boot up my PC in a way that optimises it for using MATLAB? I'm thinking that if the processor on my laptop is also doing calculations to run other programs this will slow down the MATLAB calculations. I've closed all other applications, but I know theres probably a lot of stuff going on I can't see. Can I boot my laptop up in a way that will have less of these things going on in the background?

I can't modify the code to make it more efficient.

Thanks!

Upvotes: 0

Views: 711

Answers (3)

Roy Longbottom
Roy Longbottom

Reputation: 1192

You might run some of my benchmarks which, along with example results, can be found via:

http://www.roylongbottom.org.uk/

The CPU core used at a particular point in time, is the same on Pentiums, Celerons, Core 2s, Xeons and others. Only differences are L2/L3 cache sizes and external memory bus speeds. So you can compare most results with similar vintage 2 GHz CPUs. Things to try, besides simple number crunching tests.

1 - Try memory test, such as my BusSpeed, to show that caches are being used and RAM not dead slow.

2 - Assuming Windows, check that the offending program is the one using most CPU time in Task Manager, also that with the program not running, that CPU utilisation is around zero.

3 - Check that CPU temperature is not too high, like with SpeedFan (free D/L).

4 - If disk light is flashing, too much RAM might be being used, with some being swapped in and out. Task Manager Performance would show this. Increasing RAM demands can be checked my some of my reliability tests.

Upvotes: 1

rwong
rwong

Reputation: 6162

Firstly you should perform a CPU performance benchmark on both computers.

Modern operating systems usually apply the most aggressive power management schemes when it is run on laptop. This usually means turning off one or more cores, or setting them to a very low frequency. For example, a Quad-core CPU that normally runs at 2.0 GHz could be throttled down to 700 MHz on one CPU while the other three are basically put to sleep, while it is on battery. (Remark. Numbers are not taken from a real example.)

The OS manages the CPU frequency in a dynamic way, tweaking it on the order of seconds. You will need a software monitoring tool that actually asks for the CPU frequency every second (without doing busy work itself) in order to know if this is the case.

Plugging in the laptop will make the OS use a less aggressive power management scheme.

(If this is found to be unrelated to MATLAB, please "flag" this post and ask moderator to move this question to the SuperUser site.)

Upvotes: 0

user1205577
user1205577

Reputation: 2450

There are many things that go into computing power besides RAM. You mention processor speed, but there is also number of cores, GPU capability and more. Programs like MATLAB are designed to take advantage of features like parallelism.

Summary: You can't compare only RAM between two machines and expect to know how they will perform with respect to one another.

Side note: 4 GB is not very much RAM for a modern laptop.

Upvotes: 0

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