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Randomizing with Copy/Stamp

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Hello all,


I'm rather new to Houdini and this has left me scratching my head.


My goal is to have a bunch of spheres moving up and down, as if they were bobbing on water.


I've created a field of spheres by scattering some points onto a grid and then linking a sphere into a Copy Sop. I then stamped a variable called "bobbing" with this expression: rand($PT)*sin($F*10)/3. This makes some of my spheres move more than the others.


My issue is that I can't manage to stop them from all starting this motion together and the sine curve kicks in for every one at the same time giving me the effect of a sound speaker playing. How do I get them to retain their current up-down animation while offsetting the start time?


I've tried a ForEach SOP and also a Timeshift SOP but none of them worked and I'm stumped.


I'd be grateful if you could offer any suggestions. 


I've attached the .hip file.




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You should add a point number dependent element to the phase of the sine. At its simplest, rand($PT)*sin($F*10 + $PT)/3

thank you very much eetu. I had a gut feeling it was something simple that eluded me. I did as you said and additionally multiplied it by a factor of 10 like so : rand($PT)*sin($F*10+$PT*10)/3. this creates the bouncing ball effect that i was looking for. much appreciated :)

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