The h Bar

user351417

15:00

I got a bunch of annoying comments from him under one of my Meta.SE posts about the CoC when he found people talking about his non-mainstreamness in physics chat. How creepy.

Emilio Pisanty

@ACuriousMind that framing feels discongrous to the historical process

it's not that we "don't have a level restriction"

ACuriousMind

@EmilioPisanty That's perfectly possible, I only arrived here after the formative years ;)

Emilio Pisanty

in particular, it's not that PSE never got a "bigger brother"

it's that we never got a smaller brother

i.e. MO predates MSE by quite a bit

MSE was started because MO was too strict on low-level content

not the other way around

20

Q: How did mathematics end up with two Stack Exchange sites, while Physics only got one?

I'm prompted to start this thread by a comment on a recent question about why this site has the homework policy that it does. As I said in that answer, the ecological niche that this site occupies is rather different to the one that Mathematics Stack Exchange does, and a lot of this difference is...

ditto TCS appearing before CS, but with a smaller time difference between the two

ACuriousMind

@EmilioPisanty I'm not sure how that's relevant to what I said - the status quo is that we are one site for physics of all levels. I didn't make any claim about how that came to be

I just said that this status quo makes in my eyes drawing the "non-mainstream" line harder than on sites like MO or TCS

Emilio Pisanty

@ACuriousMind it's not the content, it's the framing only

still, I'm not sure that imposing a level restriction in a split-PSE model would actually help with that problem

if you take some of our recurrent scratched-record post-on-a-loop posters

user351417

15:05

@ACuriousMind But we appear to have a strong enough downvoting culture to make sure things do not to go too far, right?

Emilio Pisanty

say, "but electron magnetic dipoles!"

or "but statistics in entanglement!"

or "but Einstein!"

(obviously only caricatures)

those would do just as much harm on either tier

they'd be drawn equally strongly to both

ACuriousMind

@Chair They're certainly getting downvoted, but the asymmetry between down- and upvotes means they usually still manage to slowly get reputation, and Emilio is probably not the only user who gets tired of interacting with such users

Emilio Pisanty

You could argue that you can then make the higher tier more strict in deleting that stuff

but then you're just shoveling the harmful stuff to the lower tier, where the only people it can harm is the beginners in the field, i.e. the people who are more susceptible to catching misconceptions from that type of contagious content

@ACuriousMind data.stackexchange.com/physics/query/840693/… for one.

Kroob.D

Please can any one explain me how geodesic explains the gravity (may the question is silly) ,without using the concept of flow of time in space -time

Emilio Pisanty

data.stackexchange.com/physics/query/393837/… for another

user351417

15:10

@EmilioPisanty I imagine I come under that, to a certain extent. I find my self arguing about factual accuracy quite rarely because I think there are a lot of cases where I suspect something's inaccurate but I don't know enough to confidently object.

ZeroTheHero

@ACuriousMind You've been active for a while on this site.. are there "natural cycles" in the quality of questions and answers?

Anonymous

@EmilioPisanty That's really what worries me.

Anonymous

While those who know enough can spot the fallacies, beginners tend to develop misconceptions rather easily. Some of the cranks have very convincing tones and specifically target the beginners.

ACuriousMind

@ZeroTheHero There is certainly a "homework" cycle that follows the beginnings and ending of parts of the academic year

user351417

@ACuriousMind And a bunch of questions about IB IA topics in December and January :P

ACuriousMind

15:12

But other than that, I couldn't pin down anything with such regularity that it would deserve to be called a cycle

Emilio Pisanty

↑ yeah, that

Kroob.D

Please can any one explain me how geodesic explains the gravity (may the question is silly) ,without using the concept of flow of time in space -time

Anonymous

@Kroob.D Please don't repeat your question. It's still visible on the screen.

ACuriousMind

@Kroob.D 1. Please don't repost messages. 2. It's not clear what "geodesic explains the gravity" is supposed to mean, nor why you'd insist on not using "flow of time".

Anonymous

In case you're not receiving any answers it's you can assume that it's either because no one is interested in it at the moment or no one here knows the answer. Usually it's the former.

ACuriousMind

15:21

And now I see that you're a sockpuppet circumventing a question-ban and a chat suspension. Goodbye.

Emilio Pisanty

@JMac well, you could review that question, for one. Though the Meta Effect is always going to do its thing.

user351417

I confess, one of those votes is mine and I regret that one... I didn't know that quantitative finance site was a thing (I cast that one a few hours back), and I thought that the too-broad reason didn't fully cover it. Unfortunately, I can't retract it.

vzn

@Chair lol sounds like zen & art of motorcycle maintenance (pirsig) a famous book/ paperback. liked it :)

user351417

If the mods have some superpower which could undo that vote, it'd be great, but considering the number of iterations of closing and reopening, I find it quite unlikely that the question will actually be reopened, so hopefully there's no harm done.

user351417

@vzn yep, that's the one.

vzn

15:28

@Chair it was a recommendation on a physics forum? are you the one entering college physics?

ACuriousMind

@Chair We could nullify the votes by reopening and re-closing, but that doesn't seem appropriate

user351417

@ACuriousMind Yes, that is quite inappropriate since the other pending close vote may be by someone who was fully aware of the circumstances and has not since changed their mind.

ACuriousMind

Exactly.

user351417

@vzn Nah, a friend who's into engineering suggested it. But yes, I'm in 12th grade and I start an undergrad physics major this fall.

vzn

@Chair its highly controversial within the physics community/ insiders but yeah outsiders might read it and scratch their heads over the commotion. in a few words author SH gores sacred cow(s)... :o

user351417

15:33

@vzn I'm still trying to get hold of it... I have other things I'd like to read right now though, so I'm not sure if I'd get around to it soon.

vzn

@Chair a high school CS teacher recommended it to me, read it over a decade later, was impressed, its nearly a classic of english literature, sold millions, should be easy/ cheap to obtain. it is intense. reminds me of movie beautiful mind about nash, strong parallels.

Emilio Pisanty

@Chair you really can't retract it?

weird

user351417

@vzn Well, the popsci sections of private libraries in India are lacking in books other than Relativity and A Brief History of Time, so no real luck. I'm not sure it's worth buying yet.

user351417

@EmilioPisanty I'm supposed to be able to? I tried once, but it said "You've already voted to reopen this question" I'll try again, maybe I was messing up something.

Jake Rose

Why is the force transmitted along a cube inside the cube? (

vzn

15:36

@Chair btw feynmans 2 popsci books are great. seems like some of this would be available in used bookstores. presumably you going to college in india?

Jake Rose

Emilio Pisanty

@Chair hmmmm, that's odd. You'd think that this would mirror the retraction of close votes, but indeed it doesn't seem to.

user351417

@vzn 1) Surely you're joking Mr Feynman barely qualifies as popsci, IMO: I think I read some of it a couple of years back and I dropped it halfway through because I was horrified that his discussion of buying women drinks and stealing doors counted as physics

user351417

2) I'm applying to colleges in the US; there aren't many Indian universities which are particularly research-oriented. The only one which has a lot of stuff going on is IISc, and that's in the city where I live, so I've always been a bit keen on not going there. Plus it's super-competitive, so there's no banking on my chances of getting in there even if I tried.

Anonymous

@Chair How was the interview btw? :)

user351417

15:45

@Blue Incredible. I had another yesterday, with a different place.

Anonymous

@Chair "Incredible" as in "amazing" or "awful"? :P

Emilio Pisanty

Hmmmmm. Anyone remember a book about looking for the senior scientist that directed the Nazi nuclear-weapons programme?

mostly a historical-thriller kinda novel

everybody was recommending it some ten-twelve years ago

Jake Rose

@Chair @vzn I don’t think many people count SYJMF as a ‘physics book’. I wouldn’t even count it as popsci. It’s more so an autobiography (although really it’s just a collection of anecdotes in chronological order but the difference is minor)

Emilio Pisanty

title was "Looking for (name)" or something along those lines

where (name) almost certainly started with K

sounded like Klingon but obviously that wasn't it

vzn

@Chair think its popsci by any reasonable defn (broadly construed) but arguments over genre in literary classification can be very subtle, generally dont believe in that. sort of like how ACM just concluded that DSs video is defn not "popsci". lol... to me popsci is not a pejorative term. along with scifi. etc!

ACuriousMind

15:48

@vzn I didn't conclude any such thing. I said it was better than most pop-sci, not that it was or was not pop-sci.

@EmilioPisanty "Looking for Klingon" sounds like the name of a Star Trek-themed speed dating event.

user351417

@Blue Awesome :P I'd mentioned that I'd heard that the interviewer was a cruel guy who was full of himself, right? So it turns out I didn't have that guy, and it was just a coincidence that they had similar-sounding names. Nevertheless, I greeted the guy who I had with the other guy's name, and he was just like "lol what the hell just happened??" and then he told me his name.

user351417

After that, I started cracking engineering jokes until I found out that he'd done a mechanical engineering major and MS in the place I was applying to. But he was such a chill guy that he took it all in good humor and he told me tonnes of cool things about the place. And I told him cool stuff about myself, so everything's hunky-dory.

Emilio Pisanty

@ACuriousMind indeed it does, hence that not being it

vzn

@JakeRose to me scientific biographies are basically popsci, think that would not be rejected by many. feynman wrote 2 "popular books about science". its in constrast/ juxtaposition to their regular scientific writing/ papers etc.

user351417

And then my interview yesterday was actually one and a half hours of my interviewer chewing up CERN propaganda the way I chew up anti-CERN propaganda (hopefully that doesn't narrow down the university name too mcuh :P)

ACuriousMind

15:51

@EmilioPisanty The title does not match, but your description would fit The One Man

Anonymous

@Chair Whoa, sounds great!

Anonymous

BTW which university's alumni was he?

user351417

@ACuriousMind The user you (?) just suspended from chat wrote a comment under one of their questions regarding the same.

ACuriousMind

@Chair Got the flag; it's handled.

Emilio Pisanty

@ACuriousMind no, that's not it

There was no Auschwitz involved

The main character spent more time in Princeton than in Germany, I think

ACuriousMind

15:53

@Chair There's (anti-)CERN "propaganda"? :P

vzn

@ACuriousMind maybe misunderstood/ misinterpreted you. are you saying you have no opinion on whether its popsci or not?

2 days ago, by ACuriousMind

But, seriously, @DanielSank, nice video. I appreciate that you're actually getting just technical enough to not distort what's happening in the way pop-sci often does.

user351417

@Blue Ah, I'm afraid I'll politely decline answering that one. Honestly, even when people in school ask me where I'm applying/what the scores are, I feel a bit weird answering those, though I have no idea why. Sorry :P

Anonymous

@Chair Oh, it's alright. No worries.

Emilio Pisanty

It included a substantial section with von Neumann in it

Also with Einstein if I recall correctly

vzn

my interpretation was "this video does not distort whats happening so therefore its not like (typical?) popsci..."

ACuriousMind

15:55

@vzn It's...probably pop-sci? But yes, I don't have a strong opinion either way

Anonymous

@Chair I too have that habit of not telling anyone until after the thing is over (in your case "getting admission"). That's totally okay. My classmates are completely opposite though. :P

user351417

@ACuriousMind Well, I modified that one to make it sound cool :P sounds much better than "anti FCC" because everyone knows what CERN is but only so many people follow the FCC issue. However, the interviewer was a comp-science person, so they were quite familiar with the stuff since they were interested in the data filtering stuff.

user351417

@ACuriousMind Cool, I just thought I'd update you on that one before it escalated. (perhaps you could delete this exchange?)

vzn

to paraphrase a recently indicted cohort of trump, think popsci is a punching bag around here. :(

@Chair ? few in physics would talk about "CERN propaganda" and thats actually at the heart of the SH dustup.

ACuriousMind

@Chair I could, but why do you think that's necessary?

@Chair True enough, I'm not even sure what "the FCC issue" is you're referring to!

Abcd

15:59

Does anyone here know CS?

user351417

@ACuriousMind It isn't necessary. I just thought one generally avoids discussing these things.

user351417

@ACuriousMind The whole thing of CERN claiming they made the same arguments to get the LHC funded... the debate about whether the FCC is worth the price tag or not.

ACuriousMind

@Chair Well, yeah, but I don't think it's a big deal here. We're already spending more time meta-discussing it than on the actual exchange ;)

John Rennie

@vzn I don't think there is an anti-popsci tendency in the h bar. There is some truly awful popsci around, but there is also lots of great popsci. Because we criticise the truly awful popsci doesn't make us anti-popsci.

ACuriousMind

I'm strongly anti-popsicle though

user351417

16:02

@vzn Well, if you're done with anti-popsci, there're plenty of good ones to talk about too! The best popsci book I've read is probably Sean Carroll's Particle at the End of the Universe. That was just before I'd decided that I wanted to do a physics major, but even after I re-read it recently, it never felt like it was awkwardly avoiding math or running away from details. However, I never got around to finding out what simplifications may have been made.

Anonymous

@ACuriousMind You're anti-icecream?!

vzn

@JohnRennie a balanced view am not in disagreement in general with but eg EP has dinged me a lot in past over just quoting scientific news as "popsci". think he even said physorg was popsci once. whatever

ACuriousMind

@Blue No, just against the abominable sub-species that are popsicles

user351417

Chaos (Gleick) was one of the bad ones IMO: as celebrated as it is (Michael Crichton said that he based a lot of Ian Malcom's dialogues in Jurassic Park upon that), the handwaving which replaced the math and graphs was a bit overwhelming.

vzn

@Blue the truth is finally revealed/ exposed, that explains so much :P

user351417

16:04

@Blue Why on earth would you call it icecream when there isn't even any cream in that stuff though???

ACuriousMind

^this ~~guy~~ chair gets it

Secret

I might need to revise my quantum textbooks again on how two subsystems of a product state, when interacting via measurement, will end up in an entangled state. I mean, sure it is very very easy to enter an entangled state or at least some mixed correlated state from a hibert space point of view since there are vastly more non product states than product state.
But still, looking at these things as density matrices, how does an interaction will jiggle the state just right to establish a quantum correlation and a mixed state

vzn

@Chair oh geez, gleick Chaos is a popular classic. :(

user351417

@vzn EmilioPisanty was just talking about how he was reading Ignition; I think that one's a popsci book.

Anonymous

Duh. Y'all sure haven't tasted the coca-cola flavored popsicles!

Emilio Pisanty

16:06

@vzn that's nowhere close to anything I've said.

Secret

I mean, like firing a photon into an electron in superposition, and you can get some partially entangled state between the photon and the electron if a measurement is performed by the photon onto the electron

vzn

@Chair am talking about years-old ~~skeletons in the closet~~ past exchanges in here :P

ACuriousMind

@Blue I don't like cola either!

Emilio Pisanty

I've criticised you for linking to mis-labelled press releases.

ACuriousMind

And don't get me started on mangoes again

Emilio Pisanty

16:06

That's nowhere close to the same thing.

vzn

lol this is very funny, quote anyone in here and they instantly show up to strongly deny it :P

user351417

@ACuriousMind I'm afraid no Indian person will let you get away with that one :P

ACuriousMind

@vzn A paraphrase is not a quote.

Emilio Pisanty

@ACuriousMind strictly speaking, this is a mis-paraphrase we're talking about

Secret

I sometimes wonder, if the measurement problem is, to explain how exactly when two subsystems in a product state become entangled when brought into some sort of contact

Emilio Pisanty

16:08

I don't see how it's funny that people object to others putting words in their mouth though

user351417

We should totally keep a counter of how many conversations we can run simultaneously.

ACuriousMind

@EmilioPisanty Huh, TIL "misparaphrase" is an actual word

Although the Wiktionary entry seems to lack citations

Secret

Some kind of information must be exchange in order to establish the quantum correlation in the first place that lead to a partially entangled state from a product state

John Rennie

@vzn you have a tendency to post links to the more sensationalist end of the popsci spectrum.

vzn

@JohnRennie lol & you have a tendency to post pictures of food.

Secret

16:12

All information is bound by the speed of light, thus that explains why the two subsystems have to be timelike separated for the correlation to be established

Perhaps:

John Rennie

@vzn the feedback I get is that people are amused by my food posts, otherwise I wouldn't post them. If I felt people were annoyed I would stop.

2

vzn

@JohnRennie lol its unanimous then! so my feedback doesnt count? what else is new around here

John Rennie

@vzn I don't recall you ever objecting to me posting food pictures.

Anonymous

Let's stop this line of conversation for a while.

Secret

When you place n subsystems of a product state close together, the hamitonian (due to some surrounding field) that can evolve the resulting n subsystem state no longer need to be delocalised over the subsystems, and hence in terms of the language of matrices, this hamitonian can rotate the n subsystem state into a partially entangled state and hence established the quantum correlation

It is certainly easier to have one hamiltonian evolve n subsystems that are placed close in space and time than to have n spacelike separated hamiltonians just happened to rotate all the n subsystems in unison into a partially entangled state

ACuriousMind

16:16

@JohnRennie amused and slightly concerned for your health ;)

Secret

Guys, is my deduction making sense here on trying to rationalise how a product state get rotated into a partially entangled state when the subsystems are placed nearby in space and time?

John Rennie

Dec 22 '18 at 9:25, by John Rennie

If you only ever eat healthy food you won't actually live longer, it will just feel like a longer time :-)

ACuriousMind

@Secret It's impossible to get an entangled state just by evolution through "n Hamiltonians" acting on the subsystems. You need a global Hamiltonian that is not the product of local Hamiltonians of the subsystems for that.

John Rennie

Currently I am doing my best (though I will probably fail) to eat an entire 2 litre tub of mint choc chip ice cream :-)

ACuriousMind

@JohnRennie good lord

Secret

16:20

ah right, the no communication rule

John Rennie

You called?

(school playground joke - sorry)

ACuriousMind

@JohnRennie I expected nothing else :)

Secret

@ACuriousMind hmm... then I am guessing the closer the states are with each other in a region (say n electron spins) the easier the system to be acted by such global hamiltonian , whereas if they are all spacelike separated, it will be very unlikely to have a global hamitonian that can rotate it to the entangled state? Basically I am trying to rationalise why entanglement is easier to occur when two quantum states are brought in close proximity

(as most entanglement production schemes do rely on the states to be somehow close to each other, such as SPD to generate photon pairs)

ACuriousMind

@Secret You need a mode of interaction for such Hamiltonians to be possible, i.e. one subsystem has to be able to affect the other - the terms in the Hamiltonian that are not "local" are precisely those we usually think of as "interaction terms". Spacelike-separated states can't affect each other.

Secret

Ah I see

interesting

John Rennie

16:27

I can do it, I just have to focus.

Emilio Pisanty

@ACuriousMind amazon.com/Search-Klingsor-International-Bestselling-Novel/dp/…

there we go

hmmm. doesn't amazon onebox? oh well

Anonymous

@EmilioPisanty No, not anymore. :/

Anonymous

@JohnRennie Good luck. Let's hope your stomach walls are stretchable. ;)

ACuriousMind

@EmilioPisanty Nope, cf. meta.stackexchange.com/q/308166/263383

@EmilioPisanty Ah, wow, "Klingon" wasn't far off :D

Emilio Pisanty

@ACuriousMind we got this recommended independently by something like seven different lecturers in our first week of uni

Anonymous

16:32

Aha, Baskin Robbins sellls Mint Chocolate ice cream here!

Emilio Pisanty

is that still a thing?

ACuriousMind

I've never heard of it

Anonymous

The color is a bit different though. I wonder why.

Emilio Pisanty

or was it just because it's originally in Spanish and had just come out?

¯\ _(ツ)_/¯

Anonymous

John Rennie

16:33

@Blue peppermint oil is colourless. The colour just depends on how much green dye the manufacturer puts in.

Anonymous

Wtf is green dye now... :P

Anonymous

Some kind of food color?

Emilio Pisanty

@JohnRennie I always wonder how food manufacturers manage to get the deep toxic red of palm oil out of all the food it goes into

John Rennie

@EmilioPisanty I don't think I've ever seen palm oil. Is it red?

Emilio Pisanty

this is in e.g. most marketed chocolate bars

John Rennie

16:36

That doesn't look all that appetising ...

Anonymous

11

A: Coloring colored ice-cream

If you make homemade strawberry ice cream, the color is likely to be very, very pale, approaching white. Green food coloring in your mix should do the trick. It would be very difficult to retroactively turn commercial ice cream a different color. The pink is almost certainly from food colori...

Emilio Pisanty

@JohnRennie to be honest, it looks a hell of a lot better in that picture than it does in person

you might struggle to find it in Chester, but I imagine Liverpool has some equivalent to Brixton Market

which will probably have it in quantity

it's usually liquid at room temperature

... in the countries where the palms grow

(and even then...)

in the UK it very often congeals into a thick sludgy paste, though

Anonymous

@EmilioPisanty Aren't there different types of palm oil?

Jake Rose

@EmilioPisanty not quite sure Liverpool does. More foreign supermarkets though so they might sell it? @JohnRennie

Anonymous

Not all of them are red afaik.

ACuriousMind

16:39

@EmilioPisanty The red is just carotene. There's lots of Google hits for "extracting carotene" so it doesn't seem to be all that hard

Anonymous

Googling tells me ethanol suffices for extracting carotene...

Anonymous

I doubt they do that.

John Rennie

I'm sure I remember reading that consuming lots of carotene colours you skin.

ACuriousMind

Useful if you want to pretend to be a flamingo :P

Loong

@ACuriousMind No more astaxanthin for you. ;-)

John Rennie

16:44

Some years back there was a children's sweet drink that had lots of carotene in it, and some especially dedicated consumers of it did actually go orange

Something "Valley". Sunny Valley? Happ Valley?

Abcd

@Blue please?

John Rennie

Sunny Delight!

Anonymous

Process for obtaining carotene from palm oil...lol, Google even has a patent on this.

Loong

@JohnRennie Any carrot juice in large amounts would work.

Anonymous

@Abcd Not really in the mood for questions now. Why not ask it to the room? Someone else might be able to answer too.

Abcd

16:50

To all: Is canonical POS the DUAL of canonical SOP form or not?

John Rennie

@Abcd according to Wikipedia they are "de Morgan duals"

Abcd

@JohnRennie never heard de Morgan dual. Let me search

Emilio Pisanty

1

Q: Classical angular momentum components are numbers. Can they be generators of some symmetry group?

In Quantum Mechanics (QM), angular momentum turn out to be the generator of rotational symmetry. This is trivial to see because in QM, angular momenta are defined by the commutation relations $$[J_j,J_k]=i\hbar\epsilon_{jkl}J_l.$$ One immediately recognises these as the generators of the rotation...

quantum-mechanics classical-mechanics angular-momentum symmetry rotation

man, we need more users like SRS asking those types of questions

Abcd

@JohnRennie I am afraid their link to "deMorgan duals" directs to deMorgan's laws...

Emilio Pisanty

those consecutive Socratic badges are extremely well-earned

heck, s/he's probably well on his/her way to a third one

John Rennie

16:55

@Abcd I think you asked me about minterms and maxterms before, and I had to give up

Abcd

@JohnRennie yeah... I know. But I can't find satisfactory answers anywhere.

Anonymous

@Abcd No. Take an example and check.

ACuriousMind

@EmilioPisanty Another item for the list "Why people should teach classical Hamiltonian mechanics properly before teaching QM"

4

Anonymous

Let's say F(A,B) = 1 only when A = 0 and B = 0.

Anonymous

Otherwise it's 0.

Emilio Pisanty

16:58

@ACuriousMind well, all those items are just variations on the same theme, innit

but yes

Anonymous

So, F(A,B) = A'B'. Now it's dual is A' + B'.

Abcd

@Blue But we should have 3 maxterms instead of 1?

Thats why its not dual right?

Anonymous

@Abcd Yes, but can you write out those maxterms explicitly?

Abcd

1 second blue

Anonymous

SOP and POS Form Examples

►

Abcd

17:03

@Blue F = (A+ B').(A'+B).(A'+B')

@Blue watched and understood already. (it doesnt cover relation between SOP and POS)

So @Blue I think we have to conclude that there's NO way to get POS from SOP algebraically w/out TT.

Anonymous

@Abcd Yes, and now can check that equals (AA'+AB+B'A'+B'B)(A'+B')=(AB+A'B')(A'+B')=A'B'.

Abcd

@Blue why complement?

Anonymous

Wait a minute. Let's take this example again.

Anonymous

> F(A,B) = A'B'. Now it's dual is A' + B'.

Abcd

yes

and it's dual's complement is:

Anonymous

17:10

(A'+B')' = A.B

Abcd

$= AB$

@Blue dual and complement are not same i think

Anonymous

@Abcd Why not take a 3 variable example and try it out yourself?

Anonymous

SOP and POS are NOT duals of each other!

Abcd

Ok let's try.

Anonymous

Tbh I'm a bit rusty on this stuff. Lemme write it out. I could be wrong.

Anonymous

17:19

Say, A+B s dual is AB while it's complement is A'B'.

Anonymous

Now, (AB)' = A' + B'.

Anonymous

A+B = A(B+B') + B(A+A') = AB + AB' + BA'

Anonymous

A'+B' = A'(B+B') + B'(A+A') = A'B + AB' + A'B'

Abcd

@Blue Is it working?

Anonymous

I mean it turns that the complement is not equal to the dual as you said. But I distinctly remember that the dual can be used to easily convert from SOP to POS. I'm misremembering something.

Anonymous

17:29

Just taking the complement and then complementing again using De Morgan's seems to work fine though. Like here.

Anonymous

3

Q: Duality Principle vs. DeMorgan Law

What is the difference between the two? Duality Principle states that any theorem in switching algebra remains true if 0 and 1 are swapped and + and . are swapped throughout. DeMorgan's Law says that any theorem remains true if the variables are complemented and + and . are swapped as well. I...

logic boolean-algebra

Abcd

@Blue it doesnt work when we have Canonicals involved.

Consider this example:

F = o'v'w' + o'v'w o'vw + ov'w

If I complement it twice, I get same thing back ...which is natural

John Rennie

17:41

... and breathe

Anonymous

@Abcd So F' = ovw'+ov'w+ov'w'+ovw (by taking the missing terms). Then (F')' = (o'+v'+w)(o'+v+w')(o'+v+w)(o'+v'+w') = F.

Anonymous

Basically, take the minterms corresponding to F=0 (instead of F=1), to get the complementary SOP.

Anonymous

In other words, POS is the complement of the omitted minterms in the SOP.

Abcd

18:02

@Blue Ah

@Blue not sure you can write F' just by taking missing minterms.

> F' = ovw'+ov'w+ov'w'+ovw (by taking the missing terms)

Blue ur this step looks wrong 2 me.

Anonymous

@Abcd Why?

Abcd

@Blue your answer is wrong acc to the book.

Answer given is:

$F= (o+v'+w)(o'+v+w)(o'+v'+w)(o'+v'+w')$

(o'+v+w') this term of your answer is not here^, rest is fine.

@Blue the thing is, even if this statement is correct do you have an intuitive + logical explanation to it?

Anonymous

@Abcd Well, F' should give you an of output 1 whenever F is 0, yes?

Abcd

@Blue yes

Anonymous

Now, imagine the truth table of F' rather than F.

Abcd

18:11

@Blue oh then it makes sense, why F' = those minterms

@Blue but why does it not give right answer?

Anonymous

@Abcd Maybe there's a calculation error somewhere. I didn't write it on paper.

Anonymous

> o'v'w' + o'v'w + o'vw + ov'w

Anonymous

What are the missing terms here?

Abcd

@Blue nothing is missing

@Blue 4 of F+ 4 of F' = 8 = 2^3

Anonymous

ovw'+ov'w'+o'vw'+ovw

dmckee

18:15

@ACuriousMind Hamiltonian mechanics was covered in my classical mechanics course, even as an undergrad. But I recall not understanding why it was useful ... I had to find the Lagrangian along the way, so this seemed like extra work.

Anonymous

24 mins ago, by Blue

@Abcd So F' = ovw'+ov'w+ov'w'+ovw (by taking the missing terms). Then (F')' = (o'+v'+w)(o'+v+w')(o'+v+w)(o'+v'+w') = F.

dmckee

And they did talk briefly about some of the useful relationships, but they came at the end of a crowded week and seemed like just more stuff memorize rather than like helpful tools.

Anonymous

Yeah, so there was a typo last time.

dmckee

It was only much later than I understood the connection to QM and realized I had to go back and repair the gaps.

Anonymous

This is just boring calculation...

Abcd

18:17

@Blue Yeah, if you believe its correct then I'll agree. But:

> In other words, POS is the complement of the omitted minterms in the SOP

What is the intution of this?

Anonymous

@Abcd I'm not really interested in this anymore. Try asking on the main site.

dmckee

@EmilioPisanty I have to say that I often find SRS's questions annoying, though I have a hard time saying why.

At least sometimes it may be because he seems to be trying to work high level concepts without haveing done the spade work to lay a proper foundation first.

Abcd

@Blue Oh I see. Thanks for the help till here.

Avnish Kabaj

$$\color{blue}{\Huge{\hbar}}$$

Took me over an year to figure that out

Anonymous

:P

Avnish Kabaj

18:24

Mod haxxing

You know in 100 years I think the world will be like the one they've depicted in ready player one

I'll even bet 10 quid

Blue is enjoying the thrill of being a graffiti artist

Anonymous

@AvnishKabaj Yesh!

Emilio Pisanty

19:00

@dmckee yeah, there's some of that

but overall they push the quality of the questions up

dmckee

19:15

Won't argue with that. They are at least looking at higher level issues.

user222141

19:44

can i ask a linear algebra question in here?

ACuriousMind

Quoth the room description: "Don't ask about asking, just ask." :)

user222141

You can find the inverse of an nxn matrix by augmenting with identity of R^n and row-reducing, but what about non-square matrices? A*M = B where all are nxn, can I row-reduce [A | M]?

ACuriousMind

For non-square matrices, you first need to say what you mean by "inverse"

They can have a left inverse or a right inverse - giving the identity when multiplied from the left or right to the original matrix, respectively

user222141

20:00

@ACuriousMind What do you mean exactly?

one inverse given by AR^(-1) and one given by L^(-1)A?

ACuriousMind

Well, for a n-by-n matrix $A$ you have that $AA^{-1} = A^{-1}A = I_n$ For a n-by-m matrix, you can ask for a left inverse $A^{-1_L} A = I_n$ or a right inverse $AA^{-1_R} = I_m$

user222141

20:13

@ACuriousMind But is it possible to augment nxn matrix A with another nxn matrix B and then row-reduce it to find M that solves AM = B like how AA^(-1) = I_n?

ACuriousMind

@user222141 I think so, but it is not guaranteed that such an $M$ exists nor that it is unique

user222141

20:39

@ACuriousMind In this case assuming A and B are both square, nxn

Anonymous

20:56

27

A: Any chance of MathJax in chat?

As a workaround while this request is pending, there exist several client-side workarounds that can be used to enable LaTeX rendering in chat, including: ChatJax, a set of bookmarklets by robjohn to enable dynamic MathJax support in chat. Commonly used in the Mathematics chat room. An altern...

Anonymous

@user222141 To render MathJax in chat you could install any one of the above bookmarklets or userscripts.

Captain Bohemian

23:06

MathJax doesn't work in Microsoft Edge.

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