Hey there,
I am in the process of learning Houdini and I have a problem with Lesson 10 of the First Steps modules http://www.sidefx.com/index.php?option=com_content&task=view&id=2202&Itemid=361 [sidefx.com] .
In the provided scene file there is an example named Particle_Disturbance which doesn't work as expected. Unlike the video example the particles always move back to their original position after they have been influenced by a force. I couldn't find a way so that it works like in the tutorial. Did I miss something here?
I'm on Houdini 13 free Apprentice Edition.

Edit: The other examples involving a force show the same behaviour. After the force stops being applied, all particles jump back to their birth position.

Have to reply to myself here. I found out that I get correct behaviour when I check “Accurate Moves” on the particle operator. But this makes the calculation of some of these examples super slow.
Is this a bug?

Not a bug.

With Accurate Births enabled, the exact sub-frame time a particle is birthed, the POP network and any dependencies are cooked/updated as well. This can be very expensive as you found out.

In H13, new POPs in DOPs POP Source DOP has a new feature that spreads the particles out at the current frame to avoid this.

Hey Jeff,
thanks for your reply. I'm a complete Houdini noob so please bear with me . In the mentioned tutorial/scene file a Particle Surface Node is used to generate the particles. As far as I can see this operator doesn't have an “Accurate Births” option.
As mentioned the “Accurate Moves” option slows things seriously down. The reason why I thought this might be a bug is because in the scene file this option is unchecked and the example doesn't work properly. Furthermore in the tutorial video everything works fine without any hiccup in the performance.

seems I'm not the only one who ran into this problem: http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=28833&highlight=force [sidefx.com]