Lammps users,
Is there a feature in LAMMPS such that when I use fix dt/reset, I can dump information every “x amount of time” rather than “x amount of time steps?”
The reason I ask is because when using fix dt/reset, the time step is constantly changing. So if I am dumping information every 100 time steps, the amount of total time between dumps will constantly be changing.
And if I want to use the neat dump image feature and convert to a movie, it would be difficult to understand what is going on as a function of time. Some parts will be drawn out and go in “slow motion” while others will go faster.
Is there a way to reconcile this?
Best Regards,
Ben
Lammps users,
Is there a feature in LAMMPS such that when I use fix dt/reset, I can dump
information every "x amount of time" rather than "x amount of time steps?"
not in exactly this way. LAMMPS *must* know how many steps away from
the current step the next frame needs to be written. you may be able
to approximate it using dump_modify every with a suitably computed
variable.
The reason I ask is because when using fix dt/reset, the time step is
constantly changing. So if I am dumping information every 100 time steps,
the amount of total time between dumps will constantly be changing.
And if I want to use the neat dump image feature and convert to a movie, it
would be difficult to understand what is going on as a function of time.
why not use dump movie?
Axel,
Yeah I know I have posted it before. I was speculating that maybe someone had developed a work-around since the last time that I asked so I thought I would at least check. Perhaps this is not good mailing forum etiquette so I will try and not repeat questions.
I have tried the dump movie command before but with not much luck. I also generally have trouble compiling LAMMPS with image writing capabilities - I think my path to the jpg header file may be off. Fortunately, the lammps-daily pre-compiled executable was updated not long ago (Aug 15 I think) and it has dump image capabilities, but not dump movies. With all this said, me not being able to use the dump movie command is not a LAMMPS issue, it’s my own issue with not downloading the right packages and putting them in the right places.
The error I get for dump movie is:
Failed to set value ‘ppm’ for option ‘c:v’
The error I get for dump movie is:
Failed to set value ‘ppm’ for option ‘c:v’
That would be an error originating in the FFmpeg command. I have tested it with the version distributed with fedora 19 and Fedora 20 as well as the precompiled windows version.
My guess is that your FFmpeg is (much?) older and thus doesn’t support the documented and recommended syntax. The command line flags to FFmpeg are compiled into Lammps and cannot be changed without recomplilation.
I (thought) I got the most recent version of ffmpeg.
I just did a command line: sudo apt-get install ffmpeg
Then recompiled LAMMPS - and that is when I got that error.
And I compiled with the appropriate flag needed for movies according to doc page.
Axel,
Yeah I know I have posted it before. I was speculating that maybe someone had developed a work-around since the last time that I asked so I thought I would at least check. Perhaps this is not good mailing forum etiquette so I will try and not repeat questions.
I think it is ok to repeat a question, if you explain why the provided previous suggestion was not satisfactory.
I (thought) I got the most recent version of ffmpeg.
I just did a command line: sudo apt-get install ffmpeg
But that is the version provided by your distribution. If you have an older distribution, it may still be an older version. But I am really speculating here. All I can say for certain is, that it works for the cases that I quoted.
I’ve been using these at least during three different lammps tutorials that I have (co-)organized during the last year.
Then recompiled LAMMPS - and that is when I got that error.
No. The error you quoted is a run time error, not a compile time error.
Yeah, I meant it was a runtime error. I meant I compiled, then ran, then got the error. Anyways, the easy work-around is to dump image and then used mencoder to combine images into a movie.
Yeah, I meant it was a runtime error. I meant I compiled, then ran, then got
the error. Anyways, the easy work-around is to dump image and then used
mencoder to combine images into a movie.
just FYI. it looks as if ubuntu may have indeed older versions of
FFmpeg for compatibility reasons.
https://launchpad.net/~jon-severinsson/+archive/ubuntu/ffmpeg
