Binary files

amtri · August 30, 2010, 11:07

Hello,

I have 2 separate questions regarding OpenFOAM binary output:

1) Is there a flag in the OpenFOAM file structure that can tell me whether binary data is written in single or double precision?

2) Also, is there a way to tell whether big or little endian is used to write the binary data in the file?

Thanks.

-amtri

alberto · September 17, 2010, 01:05

Quote:

Originally Posted by amtri

Hello,

I have 2 separate questions regarding OpenFOAM binary output:

1) Is there a flag in the OpenFOAM file structure that can tell me whether binary data is written in single or double precision?

Binary files should be written with the precision of the compiled code (double if you use the double precision solver, float if you use the single precision solver), since their purpose is not to lose accuracy when storing data.
OpenFOAM compiles in double precision mode by default.

Best,

bastil · March 15, 2011, 04:15

Quote:

Originally Posted by alberto

Binary files should be written with the precision of the compiled code (double if you use the double precision solver, float if you use the single precision solver)

Thats true. However, I am looking for a way to save meshes in double precision but run solver in single precision. Therefore, this solver needs to be able to read/write double precision. Has anybody done this before?

Regards Bastian

alberto · March 15, 2011, 23:43

What is the logic behind this? You would lose the double precision used in the mesh immediately at the first operation you force to be single precision.

bastil · March 16, 2011, 02:59

Quote:

Originally Posted by alberto

What is the logic behind this? You would lose the double precision used in the mesh immediately at the first operation you force to be single precision.

I will gain a speedup of 40%!
The accuracy differences between SP and DP for my cases are very small.
I can reproduce this behaviour with the ASCII-option: Saving my mesh with 6 digits prevents simpleFoam from running both in SP and DP but saving with 10 digits makes simpleFoam to run in both SP and DP. However SP is about 40% quicker and I don't really want to save in ASCII as it doubles the required diskspace.

Regards Bastian

alberto · March 16, 2011, 18:35

You can simply save the mesh in compressed format as ASCII, and then switch to binary for the data.

Best,

olivierG · March 17, 2011, 09:01

hello,

On some testcase i did some time ago, with a lot of time step saving, I've got the best speedup with compressed ascii file, binary file where little slower, and ascii file much slower.
so try compressed file !

olivier

August 30, 2010, 11:07	Binary files	#1
amtri New Member Join Date: Aug 2010 Posts: 15 Rep Power: 15	Hello, I have 2 separate questions regarding OpenFOAM binary output: 1) Is there a flag in the OpenFOAM file structure that can tell me whether binary data is written in single or double precision? 2) Also, is there a way to tell whether big or little endian is used to write the binary data in the file? Thanks. -amtri

March 15, 2011, 23:43		#4
alberto Senior Member Alberto Passalacqua Join Date: Mar 2009 Location: Ames, Iowa, United States Posts: 1,912 Rep Power: 36	What is the logic behind this? You would lose the double precision used in the mesh immediately at the first operation you force to be single precision. __________________ Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats (current status: http://albertopassalacqua.com/?p=1541) OpenQBMM - An open-source implementation of quadrature-based moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using.

March 16, 2011, 18:35		#6
alberto Senior Member Alberto Passalacqua Join Date: Mar 2009 Location: Ames, Iowa, United States Posts: 1,912 Rep Power: 36	You can simply save the mesh in compressed format as ASCII, and then switch to binary for the data. Best, __________________ Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats (current status: http://albertopassalacqua.com/?p=1541) OpenQBMM - An open-source implementation of quadrature-based moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using.

March 17, 2011, 09:01		#7
olivierG Senior Member Olivier Join Date: Jun 2009 Location: France, grenoble Posts: 272 Rep Power: 17	hello, On some testcase i did some time ago, with a lot of time step saving, I've got the best speedup with compressed ascii file, binary file where little slower, and ascii file much slower. so try compressed file ! olivier lifeinhand likes this.

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