0849: "Complex Conjugate"

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soren121
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0849: "Complex Conjugate"

Postby soren121 » Wed Jan 19, 2011 5:01 am UTC

Image

Alt-text: Fun fact: if you say this every time a professor does something to a complex-number equation that drops the imaginary part, they'll eventually move the class to another room and tell everyone else except you.

No idea what a complex conjugate is, but I'm assuming it's something dreaded.

EDIT: Oh, I get it now: the teacher dropped the imaginary part. Thanks to Randall for making me research my most hated subject at midnight.
Last edited by soren121 on Wed Jan 19, 2011 5:08 am UTC, edited 2 times in total.
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Re: 0849: "Complex Conjugate"

Postby meat.paste » Wed Jan 19, 2011 5:06 am UTC

I thought, "that's cute." Then I read the title text and did a simultaneous facepalm and LOL. Very nice.
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Re: 0849: "Complex Conjugate"

Postby ST47 » Wed Jan 19, 2011 5:07 am UTC

Google it.

Alternately, if you have a complex number a+bi, the complex conjugate is a-bi. So, multiplying these together gives (a^2+abi-abi-b^2*i*2)=(a^2+b^2). Which, as you'll note, happens to be real.
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Re: 0849: "Complex Conjugate"

Postby j16sdiz » Wed Jan 19, 2011 5:08 am UTC

soren121 wrote:No idea what a complex conjugate is, but I'm assuming it's something dreaded.

EDIT: I'm assuming in this problem that multiplying the waveform by its complex conjugate would yield a real number. Thanks to Randall for making me research my most hated subject at midnight.


No, complex conjugate make YOU become real.

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Re: 0849: "Complex Conjugate"

Postby shashwat986 » Wed Jan 19, 2011 5:08 am UTC

AWESOME!!!


A complex number is of the form a + ib where a and b are real number, and i=sqrt(-1)
It's conjugate will be a - ib. If we multiply them together, we get: (a + ib)(a - ib) = a^2 + b^2 which is always real.

Just thought I'd clear the air a bit.


EDIT: Whoops... Seems I'm the second guy to explain that
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Re: 0849: "Complex Conjugate"

Postby Belteshazzar » Wed Jan 19, 2011 5:11 am UTC

I have a math professor who is in the habit of saying things like "... defines a real Banach space. (pause) A real Banach space, Daddy? Yes, son, a real Banach space."

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Re: 0849: "Complex Conjugate"

Postby Mazuku » Wed Jan 19, 2011 5:13 am UTC

The maths involved here is way beyond me abd if the strip is anything to go by, is way beyond even many maths geeks, am I right?
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Re: 0849: "Complex Conjugate"

Postby Retsam » Wed Jan 19, 2011 5:17 am UTC

It's actually really not that high level of math; just moderately obscure. They're one of the most basic principles of imaginary numbers, so I think we talked about them in High School Algebra when we briefly discussed imaginary numbers.

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Re: 0849: "Complex Conjugate"

Postby Steve the Pocket » Wed Jan 19, 2011 5:20 am UTC

I'd never heard the phrase "complex conjugate" before (it sounds like a grammar term), and I only knew the term "wavefunction" from descriptions of the Schrodinger's cat thing (still don't know what it means... something to do with quantum mechanics I suppose), but I was still able to figure out that the punchline had to do with imaginary numbers.

And now that I know that quantum physics involves imaginary numbers, it makes a little more sense why people tend to find it so alien. Literally, if you happen to work for Valve.
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Re: 0849: "Complex Conjugate"

Postby Snkz » Wed Jan 19, 2011 5:20 am UTC

I'm sure many of you have seen a conjugate before. It does not have to involve complex numbers at all. Many times with fractions, multiplying the numerator and denominator by the denominators conjugate allows for some simplification tricks. Its done a lot with trig fractions.

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Re: 0849: "Complex Conjugate"

Postby Draco18s » Wed Jan 19, 2011 5:21 am UTC

Reminds me of a friend of mine who had 3 cans of Nos (energy drink) and walked into calculus and played a drinking game.

Every time the professor said, "z" he would take a shot of Nos. It was not a good day to pick "z," as every function that day was a z= function.

Hour later he was 9 shots behind and the professor had slowed down to let him catch up.

Three hours later I saw him and he was speaking so fast I couldn't understand him.

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Re: 0849: "Complex Conjugate"

Postby s0merand0mdude » Wed Jan 19, 2011 5:22 am UTC

A math/science joke I actually get! I just learned this stuff last week! Whoo for the education system!!
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Re: 0849: "Complex Conjugate"

Postby Tyrannosaur » Wed Jan 19, 2011 5:31 am UTC

j16sdiz wrote:No, complex conjugate make YOU become real.


Only in soviet russia.
Last edited by Tyrannosaur on Wed Jan 19, 2011 6:29 am UTC, edited 1 time in total.
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Re: 0849: "Complex Conjugate"

Postby Andromeda321 » Wed Jan 19, 2011 5:33 am UTC

I'm trying to figure out how sad it is that I had a friend in undergrad physics who would say this during our homework sessions for quantum. Or awesome, depending who you ask.

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Re: 0849: "Complex Conjugate"

Postby Mike_Bson » Wed Jan 19, 2011 5:34 am UTC

Since I love complex analysis, this is my new favorite comic.

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Re: 0849: "Complex Conjugate"

Postby torontoraptor » Wed Jan 19, 2011 5:40 am UTC

I just giggled for 30 seconds straight. This right here, this is why the world is awesome.*





*well this along with a myriad of other things that it would be exhaustive and rather pointless to write out
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Re: 0849: "Complex Conjugate"

Postby sedoris » Wed Jan 19, 2011 5:51 am UTC

Lol, I'm in quantum chemistry right now and we're just starting to talk about wavefunctions now. I lol'd. Thanks randall

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Re: 0849: "Complex Conjugate"

Postby sugarhyped » Wed Jan 19, 2011 5:53 am UTC

I read the comic and the alt text a couple times. Then I re-read the punch line and literally lol'ed. I surprised my self because usually im just :) or :?
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Re: 0849: "Complex Conjugate"

Postby dysprog » Wed Jan 19, 2011 6:07 am UTC

Ok, the cheese is well toasted, but I did not get the alt-text. Was there another joke that that I was supposed to see?

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Re: 0849: "Complex Conjugate"

Postby wisnij » Wed Jan 19, 2011 6:20 am UTC

Pose as a team, because... wait, wrong webcomic.
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Re: 0849: "Complex Conjugate"

Postby black_hat_guy » Wed Jan 19, 2011 6:22 am UTC

This comic would be almost as funny if real numbers were not called real. The alt-text implies that Randall has done this before to a professor, and the whole thing is kind of absurd if you think about it.
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Re: 0849: "Complex Conjugate"

Postby Eternal Density » Wed Jan 19, 2011 6:22 am UTC

Yes, multiplying something by its complex conjugate results in a real number. In this comic, Randall turns this into a terrible pun and then points out that repeating such a terrible pun will annoy people to the point that they ditch you. Thanks, Einstein. :P
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Re: 0849: "Complex Conjugate"

Postby cyanyoshi » Wed Jan 19, 2011 6:29 am UTC

Eternal Density wrote:Yes, multiplying something by its complex conjugate results in a real number. In this comic, Randall turns this into a terrible pun and then points out that repeating such a terrible pun will annoy people to the point that they ditch you. Thanks, Einstein. :P

Almost makes me want to not let Randall get away with putting such bad puns on his webcomic...



Almost.

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Re: 0849: "Complex Conjugate"

Postby pyroman » Wed Jan 19, 2011 6:32 am UTC

This one had me laughing for a good 30 sec. I got to take plenty of signals classes so I was doing this all the time much to the displeasure of everyone around me... oh who the hell am I kidding? My friends are all just as nerdy as I am. They found it hilarious as well (well at least the first few times... :? )
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Re: 0849: "Complex Conjugate"

Postby Byerley » Wed Jan 19, 2011 6:41 am UTC

It may be moderately obscure math, but it's really common in physics. In electronics and quantum especially, probably other branches too that aren't coming to mind, it's much easier to work with the functions in imaginary space, but you need to take the projection onto real space at some point to get an observable value out of it. I do it all the time, but it still took ~30s of blank staring to finally get the pun :( . Maybe I'm just bad at puns.

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Re: 0849: "Complex Conjugate"

Postby tntc » Wed Jan 19, 2011 7:06 am UTC

I have to confess, sometimes I laugh at XKCD despite having no idea what anything in the first three panels meant. That's right, shit just got fake.

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Re: 0849: "Complex Conjugate"

Postby fenrir_darkwolf » Wed Jan 19, 2011 7:22 am UTC

soren121 wrote:Thanks to Randall for making me research my most hated subject at midnight.


What's your most hated subject? Quantum mechanics? Have you taken a quantum course? It's quite nice once you get over how much maths formalism there is (not that there is anything wrong with maths formalism :P )
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Re: 0849: "Complex Conjugate"

Postby fenrir_darkwolf » Wed Jan 19, 2011 7:27 am UTC

Mike_Bson wrote:Since I love complex analysis, this is my new favorite comic.


Nice avatar btw :P. Guess we both got action this comic.
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Re: 0849: "Complex Conjugate"

Postby Max2009 » Wed Jan 19, 2011 7:30 am UTC

I hate complex numbers. I mean, calculus was hard enough to begin with, why the hell did they have to go and invent imaginary numbers? Were they deprived of imaginary friends as children and now want to get back at the rest of the world?

On topic, that was one of the worst math puns I've ever heard. Well done Randall.


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Re: 0849: "Complex Conjugate"

Postby Tetrinity » Wed Jan 19, 2011 7:46 am UTC

I actually have an Algebra exam in about an hour and a quarter, and really wasn't looking forward to it. This comic made me burst out laughing, and I must say I'm feeling quite a bit better about it. Now I just need to make sure I don't laugh everytime I use the complex conjugate of a number in the exam...

"(4-3i)/(2+i), eh? Okay, no problem, let's just multiply top and bottom by the complex conjuga- BWHAHAHAHAHAAAAAAA"

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Re: 0849: "Complex Conjugate"

Postby Mike_Bson » Wed Jan 19, 2011 8:00 am UTC

Max2009 wrote:I hate complex numbers. I mean, calculus was hard enough to begin with, why the hell did they have to go and invent imaginary numbers? Were they deprived of imaginary friends as children and now want to get back at the rest of the world?

Moments like this make me feel like the only person in the world who likes complex numbers as much as I do.

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Re: 0849: "Complex Conjugate"

Postby KShrike » Wed Jan 19, 2011 8:01 am UTC

Nice! I would love to be back in High School right now. Not so I can say it, but so I can hear someone else say it. Unfortunately, people won't be saying that statement where I am going.
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Re: 0849: "Complex Conjugate"

Postby Mapar » Wed Jan 19, 2011 8:06 am UTC

This comic had me laughing out loud, genuinely. :D I liked it.
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Re: 0849: "Complex Conjugate"

Postby Lucia » Wed Jan 19, 2011 8:29 am UTC

Once I got that the guy wasn't the professor, I chuckled.
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Re: 0849: "Complex Conjugate"

Postby NotAllThere » Wed Jan 19, 2011 9:31 am UTC

Complex numbers are very cool and interesting objects. Some infinite series don't really make sense if you only consider the field or reals. Euler's identity makes sense when it's considered as a rotation in the complex plane. They're absolutely essential to much physics and engineering and very helpful for solving certain polynomials.

Complex conjugates are used in complex division, converting it to multiplication. w/z = w/z times z'/z' = (w.z') / (z.z') = (w.z')/x Where w and z are complex numbers, z' is the complex conjugate of z, and x is a real number.
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Re: 0849: "Complex Conjugate"

Postby ramparts » Wed Jan 19, 2011 9:39 am UTC

Wow, props to Randall for three physics/astro based comics in a row (and all pretty funny ones, too). I approve!

Mazuku wrote:The maths involved here is way beyond me abd if the strip is anything to go by, is way beyond even many maths geeks, am I right?


Absolutely not - a maths geek who's graduated high school should get this.

Belteshazzar wrote:I have a math professor who is in the habit of saying things like "... defines a real Banach space. (pause) A real Banach space, Daddy? Yes, son, a real Banach space."


Your math professor sounds awesome :mrgreen:

EDIT: And apparently after 4 months of studying in England, I've taken to alternating between "math" and "maths." :facepalm:
Last edited by ramparts on Wed Jan 19, 2011 10:26 am UTC, edited 1 time in total.

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Re: 0849: "Complex Conjugate"

Postby Ronfar » Wed Jan 19, 2011 9:46 am UTC

Max2009 wrote:I hate complex numbers. I mean, calculus was hard enough to begin with, why the hell did they have to go and invent imaginary numbers? Were they deprived of imaginary friends as children and now want to get back at the rest of the world?


Amazingly enough, calculus actually gets easier when you introduce complex numbers. Trying to do calculus on functions of two or more real variables quickly becomes a real pain in the neck, but if you can use a complex function instead, things become much simpler. You don't have to worry about such things as curl, divergence, the del operator, or any of that other stuff - if the function has "is analytic" and has a derivative at all, you can find it the same way you find derivatives of real functions. And analytic functions have all sorts of other properties that make them easier to work with, too.

Also, to answer your other question, imaginary numbers were invented in order to solve cubic equations - when you plug numbers into the cubic formula, you sometimes end up having to deal with imaginary terms in the process of getting your answer, even if all three roots are real.
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Re: 0849: "Complex Conjugate"

Postby Nyerguds » Wed Jan 19, 2011 10:03 am UTC

soren121 wrote:Alt-text: Fun fact: if you say this every time a professor does something to a complex-number equation that drops the imaginary part, they'll eventually move the class to another room and tell everyone else except you.


IT'S TITLE-TEXT DAMMIT! :evil:

(...this board needs a RAAAAGE smiley -_-)

I got it from the moment I read the title text. Never done this in physics, and complex-number math has been a while ago for me.

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Re: 0849: "Complex Conjugate"

Postby Auliya » Wed Jan 19, 2011 10:32 am UTC

"Get out of my head, Randall!"

I'm studying Optoelectronics right now, and although the complex domain is nothing new for me, theese days even a simple complex conjugate can put me in a state of stupor, where I stare at the page for two minutes without actually seeing the formulae in front of me.

EDIT: @fenrir_darkwolf: I wish I hadn't noticed your avatar... there's no escape!

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Re: 0849: "Complex Conjugate"

Postby Monika » Wed Jan 19, 2011 11:20 am UTC

Meh. Old joke. Really old. Stale. There are already T-shirts with it.

But I LOL'd at the alt text :D .
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