Simulation from midway

[ytimber]

Hi,

I'm wondering whether SPlisHSPlasH can realize the following request:
Could I pass in parameters as a scene configuration file from a previous frame and continue simulation from this previous frame, rather than initializing and simulating everything from the very beginning? Many thanks in advance. It would mean a lot to me.

[janbender]

At any time in the simulation you can save the current state by pressing the key "s". You can load the state in Windows by pressing "l". Or you can load the state with the command line parameter "–state-file". A state file stores all parameter settings and the current state of all particles.

See also here: https://splishsplash.readthedocs.io/en/latest/getting_started.html

[ytimber]

@janbender
Thank you so much for the quick reply.
I’m wondering instead of using hot key to save the specific state, could I automatically save a state that I like in off screen simulation? Thank you!

[janbender]

You can also export a state each X frames. Take a look at the scene file option "enableStateExport":

https://splishsplash.readthedocs.io/en/latest/file_format.html#export

[ytimber]

@janbender
Another really quick question. I had a hard time wrapping my mind around how the state file is named. I find it a little arbitrary. It would mean a lot if you could elaborate a little. Many thanks!

[ytimber]

@janbender
Sorry to bother you with another quick question. Can I load in the state file and update viscosity/other parameters for continuing simulation?

[janbender]

@janbender Another really quick question. I had a hard time wrapping my mind around how the state file is named. I find it a little arbitrary. It would mean a lot if you could elaborate a little. Many thanks!

The name is simply: state_.bin

[janbender]

@janbender Sorry to bother you with another quick question. Can I load in the state file and update viscosity/other parameters for continuing simulation?

The simple solution is to pause the simulation when saving the state. Then you can load it, change the parameters and continue.

You can also change a parameter in the command line (–param arg), see hjere:
https://splishsplash.readthedocs.io/en/latest/getting_started.html#command-line-options

However, I didn't test this for a long time and I changed many things in the simulator. So I'm not sure if currently the command line parameter overwrites the state file or the state file the parameter. Please give me some feedback if you test this option.

[ytimber]

@janbender
Thank you for your reply.
For the state file, I didn't put it explicit enough, I meant the number string in the name after state_. What do those numbers represent?
I will test the overwrite and let you know~!

[janbender]

If you save the state at simulation time 1.05s, you will get: state_1.05.bin

[janbender]

@janbender I just tested the overwrite, the behavior of fluid still follows viscosity=0.01, which is the original viscosity set in scene configuration file, after I passed in the parameter --param Fluid:viscosity:100

I fixed that yesterday. So now it should work.

[ytimber]

@janbender
Thank you so much! I just tested -- it works!

[ytimber]

@janbender
Hi, I just encountered this problem that I have no idea how to solve.
I used the following command to do an offscreen simulation based on a past state, but with viscosity overwritten,

MESA_GL_VERSION_OVERRIDE=3.3 ./SPHSimulator /home/ccn/Downloads/SPlisHSPlasH/data/Scenes/box10.json --no-gui --no-initial-pause --stopAt 1 --state-file /home/ccn/Downloads/SPlisHSPlasH/bin/output/box10/state/state_0.600492.bin

However, it returns with an error message:
Error: StopAt parameter must be set when starting without GUI.
Didn't --stopAt 1 set the stop at parameter? This problem was not encountered when I wasn't using state-file argument in the command line. Many thanks for your help in advance! :)

[janbender]

Now this should be fixed.

[ytimber]

@janbender
Thank you so much! :))