Today I Learned

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DrGreg said:
I have long known that "xyzzy" is a magic word that can sometimes elicit the response "Nothing happens", Explanation: Xyzzy (computing)

Today I learned it has another use, as a nmemonic to remember how the vector cross product is defined: ##c_x = a_y b_z - a_z b_y##. Once you have the ##x## component, the others are obtained by cyclic permutation of the indices. Further details: Xyzzy (mnemonic)

Your post reminds me of a small desert town near the southern border between Nevada and California https://en.wikipedia.org/wiki/Zzyzx,_California familiar to drivers on Interstate route 15. :cool:
 
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This one deserves to be in here as well as the joke thread ...

eb0xwrx9fpw3ttxl9jzxqxw-_nc_ht-scontent-syd2-1-jpg.jpg
 
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fresh_42 said:
Today I found a real error on a mathematical Wikipedia page for the first time. I always thought you cannot go wrong reporting mathematical facts, but obviously you can.
what was it?
 
pinball1970 said:
what was it?
A non associative algebra is a baric algebra if and only if it has an ideal of codimension one.
+
More generally it can be shown that Lie algebras cannot be baric algebras.

This sounds reasonable each on its own, but what about solvable Lie algebras which do have an ideal of codimension one? E.g. ##\mathcal{A} = \langle X,Y\,|\,[X,Y]=Y\rangle##.

https://de.wikipedia.org/wiki/Baric-Algebra
 
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mfb said:
Why didn't you fix it?

The page hardly gets attention, the last content change was done 2008.
I tried for short but didn't find an entry point. I also assume that some additional condition was missing and since there was no reference to "it can be shown" I gave up. A correction meant work to do, although I think I have the book where it's from. But mainly, it was because I didn't manage to figure out how to make adjustments.
 
There is an "edit" button (or "Seite bearbeiten" in German). The syntax is a bit different from forums but the basics are easy to learn. Or use the discussion page. Don't worry about the formatting - others will take care of it if there is a problem. Fixing content errors is more important.
Otherwise the error will stay in there and confuse more readers.
 
fresh_42 said:
A non associative algebra is a baric algebra if and only if it has an ideal of codimension one.
+
More generally it can be shown that Lie algebras cannot be baric algebras.

This sounds reasonable each on its own, but what about solvable Lie algebras which do have an ideal of codimension one? E.g. ##\mathcal{A} = \langle X,Y\,|\,[X,Y]=Y\rangle##.

https://de.wikipedia.org/wiki/Baric-Algebra
I would feel like a fraud just liking your post as that would suggest I understood it so I will say thanks for explaining this way first. Then like it.
 
mfb said:
There is an "edit" button (or "Seite bearbeiten" in German). The syntax is a bit different from forums but the basics are easy to learn. Or use the discussion page. Don't worry about the formatting - others will take care of it if there is a problem. Fixing content errors is more important.
Otherwise the error will stay in there and confuse more readers.
Done. We'll see.
 
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mfb said:
You helped Wikipedia to become better!
Yes, you did. . . .:thumbup:

See. . . . :ok:

1556435784665.png


.
 
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BillTre said:
TIL the majority of Americans don't think Arabic numerals should be taught in schools.
View attachment 244646
Comments have been (Roman) numerous, such as this one from NY Times.
Then it is a great luck that the ciphers actually originated in India. The Arabs took them from there, and then brought it to the Mediterranean countries.

Edit: ... and the sad part is, that it was again accounting why they dropped the Roman numerals, not insight. The Italian dealers simply saw it was faster and easier.
 
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TIL that mid 90's Jeeps have a pesky security feature.

If you've had the battery out
the Engine Control Unit computer (ECU) expects the door to be unlocked with a key before driving - else it presumes a grand theft auto in progress.
So it disallows driving.
It let's the engine start and run for about two seconds
then it shuts off all the fuel injectors by discontinuing 'ground' pulses to their "low " sides..("High" sides receive battery power)
So the engine coasts to a stop.
Then the camshaft position and crankshaft position sensors obediently report to computer that engine is no longer turning,
and the computer obediently de-enerizes the Fuel Pump Relay as well an 'ASD' Relay that controls battery power to the fuel injectors.

That takes about two seconds.

symptom is it'll start and run for two seconds then die. And a little light on the dash says "Security".

Way to fix a '95 Grand Cherokee is to lock then unlock the passenger door with a key.
Computer somehow senses that and on the next start the engine continues to run just fine.
Had me going all afternoon ,
Using a test light i'd figured out that the ECU was intentionally shutting down the engine but not why... it's not in the service manual so thank goodness somebody posted it on a Jeep forum !

I wonder how many of the Jeeps in junkyards are there because of that ?
It'd likely be mis-diagnosed as faulty Engine Control Unit which is a really expensive part.
I noticed in the Denver junkyard almost all the Jeep ECU's were gone.

i really dislike computers in cars...

old jim
 
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Not exactly related, but in a similar vein, I rented a van once, back when I had little enough stuff that I could DIY a house move. Got it back to my place and discovered there was no keyhole in the cargo door. No amount of prodding anything revealed a hatch cover that might conceal one, so I rang the rental place. Turned out you unlocked the cargo door by unlocking the driver's door twice. They did apologise for forgetting to mention that...

Edit: today is not the first day you could have learned this. I appear to be running short on personal anecdotes o0).
 
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I noticed that I am a pf molecule the other day and I thought it was very sweet. We are all just molecules in the wonderfully rich tapestry that is physics forums. However, when checking where posters were from on another thread I realized this is not the case. Checking out the big hitters we have a mountain, an ocean, a moon and Fresh42 is a singularity!
 
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pinball1970 said:
Checking out the big hitters we have a mountain, an ocean, a moon and Fresh42 is a singularity!

And I'm an Armchair Scientist. o0)
 
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TIL that I am what? A singularity?
Drakkith said:
And I'm an Armchair Scientist. o0)
You can still become a Couch Potential, a Big Bangjo Player, a Rocking Chair Asteroid, a SOFIA astronomer ...
but me, as a singularity ... my only hope is they will find a white hole some time. :frown:
 
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fresh_42 said:
TIL that I am what? A singularity?

You can still become a Couch Potential, a Big Bangjo Player, a Rocking Chair Asteroid, a SOFIA astronomer ...
but me, as a singularity ... my only hope is they will find a white hole some time. :frown:
If this is a mass thing then you are infinitely larger than me. Greg would not give me details on rankings and suggested I search and work them out. I have to aim for organism next apparently. It could be worse, I could be a baculum.
 
fresh_42 said:
... or even worse: a baubellum!
Yes that's worse..
 
Do we have a black hole?
[Designated as such; not "just" 'singularity' ...]
 
Stavros Kiri said:
Do we have a black hole?
[Designated as such; not "just" 'singularity' ...]
I've not seen one.
I'm checking members mass status out as I read threads...on a Friday night...
 
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pinball1970 said:
members mass status
Is it a mass thing or more like a "structure thing"? ...
 

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