Why is c++ taking longer than MATLAB?

rleader · April 25, 2017, 03:36

Comparing my run times with other people coding the same method is revealing that my c++ code is taking about 30% longer than their MATLAB codes when it should be much, much faster. I cannot seem to figure out why is this.

I use Visual studio 2015 community as my compiler.

I use of Ox (full optimization).

My hardware is comparable to my peers.

Anyone have any ideas?

akidess · April 25, 2017, 04:00

You wrote poorly optimized code.

Abderahmane · April 25, 2017, 14:14

Well from what i know, is that i compared once codes : Python & Matlab & Fortran , the Fortran is the most faster.

To answer your question :

you can install ( openmpi ) than try some tutorials to make your code parallel and if your machine has 4 processors your code will be 4Xtimes faster

flotus1 · April 25, 2017, 14:23

If he managed to get slower execution in c++ than in matlab I don't think parallelization is the next logical step.
He should really investigate what slows down his code, for example by using a profiling tool.

LuckyTran · April 25, 2017, 20:47

For many built-in functions, Matlab accelerates the routine by running them in parallel. I.e. max, min, etc. Is your c++ purely serial? Are you even comparing the same code?

abkahraman · April 30, 2017, 12:05

Since you are using Visual Studio, if you forgive me for being so obvious, are you sure you are "running" the code? Perhaps you are debugging the code using built in F5 (at least this was the way it was in an older Visual Express) so the IDE is actually losing time debugging your time. You might want to try reaching the directory where your .exe file is and run it from there perhaps?

Wingman · April 30, 2017, 13:34

I don't know how your code is or what it does. Are they using sparse matrices in Matlab? They reduce the calculation allot.

April 25, 2017, 03:36	Why is c++ taking longer than MATLAB?	#1
rleader New Member Rob Join Date: Apr 2017 Posts: 1 Rep Power: 0	Comparing my run times with other people coding the same method is revealing that my c++ code is taking about 30% longer than their MATLAB codes when it should be much, much faster. I cannot seem to figure out why is this. I use Visual studio 2015 community as my compiler. I use of Ox (full optimization). My hardware is comparable to my peers. Anyone have any ideas? Ankit Sharma likes this.

April 25, 2017, 04:00		#2
akidess Senior Member Anton Kidess Join Date: May 2009 Location: Germany Posts: 1,377 Rep Power: 29	You wrote poorly optimized code. __________________ On twitter @akidTwit Spend as much time formulating your questions as you expect people to spend on their answer.

April 25, 2017, 14:14	parrallel solution	#3
Abderahmane New Member A.MAROUF Join Date: Dec 2016 Posts: 22 Rep Power: 9	Well from what i know, is that i compared once codes : Python & Matlab & Fortran , the Fortran is the most faster. To answer your question : you can install ( openmpi ) than try some tutorials to make your code parallel and if your machine has 4 processors your code will be 4Xtimes faster Ankit Sharma likes this.

April 25, 2017, 20:47		#5
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,668 Rep Power: 65	For many built-in functions, Matlab accelerates the routine by running them in parallel. I.e. max, min, etc. Is your c++ purely serial? Are you even comparing the same code? KaLium likes this.

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April 25, 2017, 14:23		#4
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	If he managed to get slower execution in c++ than in matlab I don't think parallelization is the next logical step. He should really investigate what slows down his code, for example by using a profiling tool.

April 30, 2017, 12:05		#6
abkahraman New Member Ali Berk Kahraman Join Date: Dec 2015 Location: Braunschweig, Germany Posts: 13 Rep Power: 10	Since you are using Visual Studio, if you forgive me for being so obvious, are you sure you are "running" the code? Perhaps you are debugging the code using built in F5 (at least this was the way it was in an older Visual Express) so the IDE is actually losing time debugging your time. You might want to try reaching the directory where your .exe file is and run it from there perhaps?

April 30, 2017, 13:34		#7
Wingman Member William Join Date: Aug 2016 Posts: 56 Rep Power: 9	I don't know how your code is or what it does. Are they using sparse matrices in Matlab? They reduce the calculation allot.