[afilter, analog filter applet] "Options" > "Show Poles & Zeroes" not working

[zach-lol]

Hello!

Sorry if this isnt the right place to put this. I am not very familiar with GitHub & I didnt see a repository for the analog filter applet (afilter).

Recently I have been using the Analog Filter Applet (falstadcom/afilter/). I have been playing around with it, trying to see what it is capable of. Something that caught my eye was "Options" > "Show Poles & Zeroes". When I click it, it appears as though nothing happens. All that I notice is that:

1. the entire circuit shifts to the left
2. the right hand side of the screen becomes unusable (cannot place or drag components over to it).
   I guess my expectation would be that the bode plot on the bottom would be marked with X'es and O's for poles & zeros respectively.

The only way I could get the feature to work is:

1. clicking the initial link you get from googling "falstad analog filter", so that the starter RC circuit with the cap having the "cutoff frequency" slider.
2. When "Options" > "Show Poles & Zeroes" is clicked, then a plot shows up on the right, and a line traces over it when hovering over the bottom bode plot.
3. If I try to add another capacitor to the circuit, it breaks, and I can get neither the right hand side plot nor the bottom right hand side "Poles: _" info to show up again

Questions:
*Not sure what the plot on the right is, what its units are, or how to read it.
*Not sure why it only works when that one cap with the slider is in the circuit.
*Is there something I am missing?

[pfalstad]

I answered this already in private email but I'll put my answer here for future reference..

I never really finished the analog filter applet. It doesn't calculate the poles and zeros for an arbitrary circuit. It only works for the predefined filters.