Monday, June 8, 2020

Zoom on Linux

Thanks to the pandemic, I'm been spending a lot of time on Zoom lately, and I'm grateful to have it. The Zoom Linux client seems to be almost as good as the other clients. The only thing that I know is missing is virtual backgrounds, which I do not particularly miss.

That said, I did run into one minor bug (I think). It has to do with what I think is called the "panel". (I've found it strangely hard to confirm this, despite a good bit of searching.) What I'm referring to is a widget that sits off to one side (and can be moved by me) when Zoom is running full screen and a presenter is holding the "spotlight" (owning the bulk of the window). The panel has four buttons at the top that let me choose its configuration. Three of them will show just my video (small, medium or large). The fourth one will show a stack of four videos, each a participant (excluding the presenter), with mine first and the other three selected by some rule I cannot fathom. (Empirical evidence suggests it is not selecting the three best looking participants.) Showing my camera image isn't exactly critical, but it's somewhat reassuring (meaning I know my camera is still working, and I'm in its field of view).

I'm running Zoom on both a desktop and a laptop, the latter exclusively for online taekwondo classes. On my desktop, the panel behaves as one would expect. On my laptop, however, the panel window assigned to my camera was intermittently blanking out. Randomly moving the cursor around would bring the image back (temporarily). This happened regardless of what panel configuration or size I chose.

On a hunch, I disabled the screen lock option on the laptop (which would normally blank the screen or show a lock screen if the laptop sat idle for too long. To be the clear, even with no keyboard/mouse input from me, the laptop was not showing the lock screen or sleeping -- the main presenter was never interrupted. It was just my camera feed that seemed to be napping. That said, disabling the lock screen seems to have helped somewhat. If the panel is showing only my camera, it still blanks after some amount of "idle" time; but if the panel is set to show a stack of four cameras (including mine), mine does not seem to blank out any more.

It's still a mystery to me why mine blanks when it's the only one in the panel, although it's clear there's a connection to my not providing any keyboard or mouse input for a while. The blanking never happens on my desktop. They're both running Linux Mint (the laptop having a somewhat newer version), and they're both running the latest version of the Zoom client. The laptop has a built-in camera whereas the desktop has a USB webcam. The desktop, unsurprisingly, has a faster processor, and probably better graphics. My typical desktop Zoom usage does not involve extended periods of inactivity on my part (if I'm not doing something useful as part of the call, I'm surreptitiously checking email or playing Minesweeper), so the lack of blanking on the laptop may just be lack of opportunity. It might be a matter of the desktop having better hardware. It might just be some minor computer deity figuring it's more entertaining to annoy me during a workout than during a meeting. Anyway, turning off the screensaver got rid of at least part of the problem. If anyone knows the real reason and/or the right fix, please leave a comment.

Monday, June 1, 2020

An Idea for an Agent-Based Simulation

I don't do agent-based simulations (or any other kind of simulations these days), so this is a suggested research topic for someone who does.

A number of supermarkets and other large stores have instituted one-way lanes, presumably thinking this will improve physical distancing of customers. I just returned from my local Kroger supermarket, where the narrower aisles have been marked one-way, alternating directions, for a few weeks now. The wider aisles remain bidirectional (or multidirectional, the way some people roll). Despite having been fairly clearly marked for weeks, I would say that close to half of all shoppers (possibly more than half) are either unaware of the direction limits or disregard them. Kroger offers a service where you order online, their employees grab and pack the food (using rather large, multilevel rolling carts), and then bring it out to your waiting car. Kroger refers to this as "Pickup" (formerly "Clicklist"). Interestingly, somewhere between 70% and 90% of the employees doing "Pickup" shopping that I encountered today were going the wrong direction on the directional aisles.

My perhaps naive thought is that unidirectional aisles are somewhere between useless and counterproductive, even if people obey the rules. That's based on two observations:
  1. the number of people per hour needing stuff from aisle 13 is unaffected by any directional restrictions on the aisle; and
  2. obeying the rules means running up extra miles on the cart, as the shopper zips down aisle 12 (which contains nothing he wants) in order to get to the other end, so that he can cruise aisle 13 in the designated direction.
Of course, OR types could mitigate item 2 by solving TSPs on the (partially directional) supermarket network, charitably (and in my case incorrectly) assuming that they knew which aisle held each item on their shopping list (and, for that matter, charitably assuming that they had a shopping list). I doubt any of us do have supermarket TSPs lying around, and that's beyond the skill set of most other people. So we can assume that shoppers arrive with a list, (mostly) pick up all items from the same aisle in one pass through it, and generally visit aisles in a vaguely ordered way (with occasional doubling back).

If I'm right, item 1 means that time spent stationary near other shoppers is not influenced by the one-way rules, and item 2 means that time spent passing shoppers increases (because shoppers have to log extra wasted miles just getting to the correct ends of aisles). So if any of you simulators out there would care to prove my point investigate this, knock yourselves out, and please let me know what you find.

Addendum: I heard an interview with Dr. Samuel Stanley, the current president of Michigan State University, regarding plans for reopening in Fall 2020. During the interview, he mentioned something about creating one-way pedestrian flows on campus. (Good luck with that -- herding undergrads makes herding cats look trivial.) The logic he expressed was that it would reduce face-to-face encounters among pedestrians. Dr. Stanley's academic field is infectious diseases, so presumably he knows whereof he speaks. On the other hand, my impression from various articles and interviews is that droplets emitted by COVID-infected people can linger in the air for a while. So there is a trade-off with one-way routing: an infected person passes fewer people face-to-face, but presumably spreads the virus over a greater area due to longer routes. Has anyone actually studied the trade-off?