How to read data from external file

Hello,

I must say that your problem is not very clear to me. Could you please be
more specific or perhaps post a short script describing your problem more
in detail?
Anyway, if computational costs is an issue for you, do not do file
manipulations each time step.
cheers
Jan

2014-02-18 17:51 GMT+01:00 rayolau <email address hidden>:

> New question #244203 on Yade:
> https://answers.launchpad.net/yade/+question/244203
>
> Hi mates!
>
> I've made a function which calculates the applyinf force to different
> particles in function of some variables (shape, mass...). However,
> appliying this function each time step results in a huge computational cost
> (time) that i can´t afford. So I've decided to call this function each
> 100000 time steps and save the resulting forces with their corresponding
> Ids to be constant applied during the 99999 other iterations.
>
> So, which is the best way to deal with the problem??? I was thinking about
> saving the particle Ids and their corresponding forces in a external file
> and call it each one of the 99999 remaining iterations. That is made with a
> defined function that reads the data and assigns the corresponding force to
> the corresponding particle Id.
>
> But maybe it would be better to use the addData function... Anyways, I
> don't know the best way to read (not to save) an external file (I'm a
> python newbie :S).
>
> I would be very grateful for any kind of help.
>
>
>
> --
> You received this question notification because you are a member of
> yade-users, which is an answer contact for Yade.
>
> _______________________________________________
> Mailing list: https://launchpad.net/~yade-users
> Post to : <email address hidden>
> Unsubscribe : https://launchpad.net/~yade-users
> More help : https://help.launchpad.net/ListHelp
>

Hi,

For reading a file from Yade, give a look to the python code of ymport.textExt() function, in https://github.com/yade/trunk/blob/master/py/ymport.py from line 13.

The reverse operation (writing in a file data concerning your force) will be easy if you look to export.textExt() in https://github.com/yade/trunk/blob/master/py/export.py, from line 10

But, if you do not quit your yade session, you can indeed use a python variable, that you set / use when needed.

But probably there is a 3rd method, more straightforward, to keep these forces acting on your bodies : give a look to https://www.yade-dem.org/doc/yade.wrapper.html#yade.wrapper.ForceContainer.permF
(I never used it, so I can not tell you more at the moment)

I guess you will succeed !

Jérôme

It sounds like the use of text files would overkill.
This should be enough:

for b in O.bodies:
   #define your force for body b
   O.forces.addF(b.id,force,permanent=True)

O.run(100000,1)

for b in O.bodies:
   #define new forces
   O.forces.addF(b.id,force,permanent=True)

etc.

Maybe use a PyRunner:

def addForces():
 for b in O.bodies: # if the force is only applied to specific forces use a defined list instead of O.bodies
  f=... # your force vector, you can calculate it here
  O.forces.addF(b.id,f,True)

O.engines=[
 PyRunner(initRun=True,iterPeriod=100000,command='addForces()'), # will be called every 100000 time steps
 ForceResetter(),
 ... # your engines
 ]

etc.

Klaus