Cant see any issues with the bullet solver, Seems to work ok here.
Apart from some of the objects falling out of bounds

Check if your merge node is set to "mutual" for Affector relationship.

Are you able to share the hip file to look at?

Has the viewport glitched?

Maybe refreshing with "labs" menu, "reset viewport" will help

Use a RBD solver instead of Vellum.

1, Create sphere
2, rbdconfigure node
3, rbd bullet solver

Turn on and increase the "user bounce" under physical attributes on the "RBD configure" node.

I haven't come across a function that sets the amount of decimal places or UI option that tells Houdini to be less
accurate but this can be done using vex or an expression.

For point locations or any value that you want to round to something a little less precise than:

-8.742277657347586e-8..... -0.00000008742277657347586.

Multiply the value by 10000 for example then use the "rint" function in vex or the "round" expression to round the
value to the nearest integer then adjust the decimal places back again by multiplying by 0.0001

Interesting question, My guess would be floating point imprecision.

It's likely down to the way this circle node point locations are actually created I would imagine using sin, cos
to plot each location......so the divisions in the underlying code would be mathematically calculated as steps around a circle
rather than a fixed start and end point.

As you are probably aware as accurate as computers are they are not quite perfect, is anything?, it can be impossible to calculate infinite accuracy, eventually the precision will run out of steam unless the app was specifically designed to deal with ridiculously high precision, which is where the mathematical variable "epsilon" is used for error bounds with very precise calculations that breach the accuracy boundary that an 32,64,1024 bit values can deal with.

Hopefully this comes close (no pun intended :P) too an answer why we get the tiny, tiny difference between -8.742277657347586e-8 and 0.0 when using this way of creating an arc using the circle node.

-8.742277657347586e-8 as a real number is -0.00000008742277657347586.


To get the values as you expected if necessary use a fixed start and end point for an arc.

To achieve this use the curve node set to bezier and while drawing the curve use "a" to create an arc
so you can have the exact start and end point.

if you were a mathematician that enjoys finding "discrepancy's"......or an accountant.....you could probably find
one of the points between the start and end locations along the arc might not be quite accurate to 8238764850856308508768653408 decimal places but the computer and the apps are doing the best they can.


Hope this helps!

Firstly check the source of the group, if you didn't create it directly yourself what caused it to be made?
Many times it's a more complex node doing a lot of work for us under the hood where a quick double check of it's
initial setup is preferable to changing what's in these groups further down the line if something seems a bit off.

There are more ways to amend and adjust group selections other than my explanation in the previous post which
was geared towards interactive selections.


A few methods that come to mind that are more "procedural"


"Group_Combine" node pretty much speaks for itself.

Creating another group node with the same name as the incoming group "see initial merge" on the node parameters.

Add or removing elements from a group using a VEX wrangle.

you'll notice the point group from the point wrangle wont appear in the viewport like viewing a group node shows them.

If you didn't already know hit the "display group and attribute list" icon for a more reliable view of group selections.
(right side of the viewport.


Cheers!

I think you're asking about reselection?

For example by pressing the triangular arrow head icon to the right of the parameter, make a new selection in the viewport , SHIFT+ to add to selection, CTRL+ to remove....lock in new selection by pressing "Enter"

Or

Select a node press "`" to enable reselect mode.....on my keyboard its the key to the left of "1" top left, it can differ sometimes depending on keyboard layout for your location in the world.

Reselection causes some confusion while learning.....it will work as expected by having the blue tab on the active node and the "showhandle" icon is activated *not* the "select" icon.....left side of viewport.

The quick shortcut to activate the "show handle" icon for any selected node is by pressing enter.

Remember to press "Enter" after making a new selections!

------------

It's a bit of a gotcha as *showhandle* is not what many at first think it is, it's not for showing basic transform axis handles.......it will however show handles, selections, options etc that are relevant with the current node

A good way to fully understand this is drop a curve node.....you'll see if the "select" icon is active its just for selecting....no curve functionality can be used even though you're active on the curve node......by selecting the "show handle" icon you'll now see and be able to use all the options and functionality related to the curve node.

Is it confusing at first, hell yeah.....though once you understand the distinction between the two it's actually a great
way of working.


Hope this helps!

Adding rotation to the translation of the collider has increased the overall "movement speed"

In this case adding substeps will help, each frame will be split into the amount of substeps,
effectively making the simulation more accurate though unfortunately also take longer to process.

Don't have the collision object so it's intersecting the cloth at the start of the simulation.
Also to get a pretty good result without requiring extra sub steps on this occasion increase "Collision passes"

Adding a "popproximity" node to the particle sim which will create a "nearestdist" attribute on each point/particle that can be read using a "popwrangle".....if its in range etc then set the attribute "life" = 0 or "dead" = 1 to kill the particle.

The reason for it is that you have "ghost other objects" turned on for the viewport.

Unless it's set to "Hide other objects" you're also seeing the LOPs display, currently USD curves default
to a width of 1 if not specified, which is why the large ribbons appear.

Oh my.....I was not expecting this and so well explained....brilliant!
How on earth did you manage to figure this out?

Got to wonder why are there sooooooo many options the UI could take advantage of and doesn't.



Confirming it sure does work........too much??

Ah gotcha...just briefly looked for a chance that the global UI scale or network view display options maybe had something but as you said seems like nada.

I have seen people do some pretty funky things in the network view with python, perhaps that's an option.....I would be interested if you find anything as I just picked up a new 4k monitor and had not even really noticed.....until NOW!

If I understand you the blue display/render flag is active on for example a sphere node and you select/activate another node like for example a box node and want to change how this active node is viewed?

To do this press "d" in the viewport..."markers tab"

"set display options for" : current model geometry

Then change the drop down menu under "draw" to whatever you prefer.

You're currently at the "Object Level".

Create a "Geometry Node" and double click on it to go inside you'll see your level changes from "Object" to "Geometry" (top right of the network view).....The Skeleton node will then be available.

Sometimes certain nodes can only be created in a specific context, a little confusing at first but it soon makes sense as you dig deeper.

One method for getting a value of a channel from chops into a vex wrangle requires creating a parameter on the sop wrangle using the "parameter edit menu", give it a data name / label, then use an "export" node from inside chops to link to the new parameter.

Turn on the orange tab (second from left) on the export node which will override your new parameter then you can access it inside vex.

There maybe a few other/better ways I am not aware of but this does work for wrangles.

**********

If you simply need to read the value of a channel into a parameter in SOPs for example you can use the chopcf() function to read any channel value at any given time directly.


Also look into the "channel sop" in combination with a "geometry node" from in chops to pull in existing data, manipulate the channels in sops with a math node and waveform or whatever and return them back to sops using the channel sop, it will overwrite the existing data from sops with the chop modified version.....this allows many channels to be adjusted at the same time....cool for delay effects, offsets etc.

The first clip is what I thought you were asking but in hindsight....I think I get you now ^^

How I got equal lengths was hit the "tie handle" option to get a straight control as in your image where both
have differing lengths, select only the first "tie point" copy the Accel value from the bottom of that panel
into the second tie handle.....this will make the lengths equal (I think)

To adjust the curve from there turn on "Untie Values" not "Untie Handles" and select the actual "line" linking the key to the "tie handle" to rotate the handle around the key maintaining length.

The next button along, "Un-tie" handles

Personally I would keep it as simple as possible when learning Houdini and stick with just using basic nodes, it's pretty mind blowing how much can be achieved with them.

If you *really* want to learn the math of 3D ...urgh, I remember being there....A great little book that I can recommend as a starting point is '3D Math Primer for graphics and game development' it has lots of diagrams and example explanations of most
of the formulas to give you a good start.