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mdklatt
1/11/2006, 03:53 PM
A system of equations in (x, y, z):

A = x - y
B = x - z
C = z - y

There are three equations, but none of them contain all three variables so I'm screwed, right?

RacerX
1/11/2006, 03:54 PM
no.

Fugue
1/11/2006, 04:00 PM
FermacerX

mdklatt
1/11/2006, 04:01 PM
no.

No, I'm not screwed? Please explain. I keep trying to solve the bastards (by hand) and keep getting identities or the variable cancel each other out.

FirstandGoal
1/11/2006, 04:01 PM
Too many years and too many beers to help ya there

mdklatt
1/11/2006, 04:05 PM
N/M

yermom
1/11/2006, 04:06 PM
B=A-C?

proud gonzo
1/11/2006, 04:07 PM
what are you solving for?

C + B = A

Stanley1
1/11/2006, 04:09 PM
True?

mdklatt
1/11/2006, 04:09 PM
My coefficient matrix has a zero diagonal in it. I think that's bad.

yermom
1/11/2006, 04:10 PM
i'm not sure. but yeah, it might be

achiro
1/11/2006, 04:11 PM
D=All of the above

Howzit
1/11/2006, 04:14 PM
42

mdklatt
1/11/2006, 04:17 PM
what are you solving for?



(x, y, z)

I think this system is underdetermined. :mad:

Mjcpr
1/11/2006, 04:18 PM
Examine Your Zipper!!!!


Hahahhaahah!!

Howzit
1/11/2006, 04:21 PM
I did determine that A = A, B = B, and C = C if that's any help.

1stTimeCaller
1/11/2006, 04:22 PM
a combination of A and B can be C, if done correctly.

Harry Beanbag
1/11/2006, 04:40 PM
When in doubt, the answer is always C.

KABOOKIE
1/11/2006, 04:42 PM
A system of equations in (x, y, z):

A = x - y
B = x - z
C = z - y

There are three equations, but none of them contain all three variables so I'm screwed, right?

I count 6 variables. But, if you want terms of ABC then sure you can solve this.

FirstandGoal
1/11/2006, 04:51 PM
Is thread making anybody else think of the Jackson 5?

mdklatt
1/11/2006, 04:53 PM
I count 6 variables. But, if you want terms of ABC then sure you can solve this.

A, B, and C are constants. The problem is that none of the three equations contain all three variables. The determinant of the coefficient matrix is 0; I'm pretty sure that's bad.

Widescreen
1/11/2006, 04:54 PM
220. Or 221, whatever it takes.

Howzit
1/11/2006, 05:07 PM
I've gotta brush up on my guzintas.

Mjcpr
1/11/2006, 05:08 PM
I've gotta brush up on my guzintas.

Is that some kind of manscaping?

Howzit
1/11/2006, 05:10 PM
Guzintas.

2 guzinta 4 2 times.
2 guzinta 6 3 times.

Damn, boy, ain't you ever heard of Jethro Bodine?

skycat
1/11/2006, 05:10 PM
Your system implies that B+C=x-y=A. In other words, you don't have three independent equations.

I think that's what it means anyway, I'd just use matlab. :D

mdklatt
1/11/2006, 05:22 PM
In other words, you don't have three independent equations.



Yeah, that's what I said--my coefficient matrix is singular.

skycat
1/11/2006, 05:25 PM
Yeah, that's what I said--my coefficient matrix is singular.

Well, if you're just asking whether that's bad or not, the answer is yes. :O

GottaHavePride
1/11/2006, 05:33 PM
Yeah, I came up with A-B = z-y = C. So you're SOL. You can solve for x in terms of z and y, but that's about it.

skycat
1/11/2006, 05:42 PM
By the way, it's not unsolvable because all three variables don't show up any any single equation. There are plenty of sets of equations that would still be solvable.

For instance, you could solve for your three equations if you changed the sign of either variable in your first equation.

mdklatt
1/11/2006, 05:50 PM
For instance, you could solve for your three equations if you changed the sign of either variable in your first equation.

You obviously don't comprehend what's at stake here. If go chaning signs around people could die. Did you hear me? People. Could. DIE.


:D

Harry Beanbag
1/11/2006, 05:50 PM
My coefficient matrix has a zero diagonal in it. I think that's bad.



This may help with that. (http://www.levitra.com/)


YWIA

yermom
1/11/2006, 06:26 PM
seems like A=B+C is the answer

any A, B, and C that satisfies A=B+C will work

like 3,2,1 or 5,3,2 or 100,25,75

skycat
1/11/2006, 06:31 PM
seems like A=B+C is the answer

any A, B, and C that satisfies A=B+C will work

like 3,2,1 or 5,3,2 or 100,25,75

Except that A, B, and C are known constants. He needs to come up with another independent equation in order to solve for x, y, and z, and apparently prevent much wanton destruction.

mdklatt
1/11/2006, 06:35 PM
Except that A, B, and C are known constants. He needs to come up with another independent equation in order to solve for x, y, and z, and apparently prevent much wanton destruction.

My three planes intersect as a line, not a point. :(

yermom
1/11/2006, 06:40 PM
this is bad for us, isn't it?

should i be looking for a basement now?

mdklatt
1/11/2006, 06:47 PM
this is bad for us, isn't it?



I don't know about you, but a world where the Total Ozone Portable Spectrometer calibration coeffecients for each individual wavelength are unknown is not a world I want to live in.

yermom
1/11/2006, 07:03 PM
CRAP!

RacerX
1/12/2006, 12:16 AM
Nobody said anything about lines. This is in Wal-Mart, isn't it?

afs
1/12/2006, 12:23 AM
what in the heck is this for?

critical_phil
1/12/2006, 12:25 AM
http://x12.putfile.com/1/1018151296.jpg (http://www.putfile.com)

Penguin
1/12/2006, 07:46 AM
My three planes intersect as a line, not a point. :(

Wait a minute! Nobody mentioned anything about planes.

Did you take into account that there is no drag on an airplane when flying in a vacuum?

mdklatt
1/12/2006, 10:24 AM
what in the heck is this for?

If you really want to know I'll tell you....

:eddie:

Stanley1
1/12/2006, 10:27 AM
Wait a minute! Nobody mentioned anything about planes.

Did you take into account that there is no drag on an airplane when flying in a vacuum?

Where did the vacuum cleaner come from? :confused:

Penguin
1/12/2006, 02:56 PM
Where did the vacuum cleaner come from? :confused:

That's the secret for solving algebra problems.


You don't want to know what I had to do to solve differential equations.

yermom
1/12/2006, 04:11 PM
If you really want to know I'll tell you....

:eddie:

i'm fairly curious as well

i got as far as figuring out why they intersect at a line and not a point, but i couldn't quite put together what the line was

FirstandGoal
1/12/2006, 04:23 PM
Ok, so when you guys get this figured out, can you move on to world peace or something?

skycat
1/12/2006, 04:38 PM
i'm fairly curious as well

i got as far as figuring out why they intersect at a line and not a point, but i couldn't quite put together what the line was

Well, I don't think he was quite right about that. The reason that there isn't an explicit solution is that he has equations describing lines in each of the three planes of a 3D cartesian space. A plane would be described if all three variables were in any one of the equations.

And while it is possible for three lines in three planes to intersect, they don't in this case.

mdklatt
1/12/2006, 04:40 PM
i'm fairly curious as well

i got as far as figuring out why they intersect at a line and not a point, but i couldn't quite put together what the line was


Any equation in three-space (x, y, z) describes a 2-D plane. Unless they are parallel, the intersection of any two planes (call them A and B) is a line. Now add a third non-parallel plane (C) to the mix. The intersection of A and C is a line (call it ac). The intersection of B and C is another line (call it bc). Lines ab and ac have to intersect at a point. The coordinates of this point satisfy all three equations. In my situation, the lines of intersection (ac and bc) happen to be the same line so there are an infinite number of solutions that satisfy all three equations.

mdklatt
1/12/2006, 04:42 PM
Well, I don't think he was quite right about that. The reason that there isn't an explicit solution is that he has equations describing lines in each of the three planes of a 3D cartesian space. A plane would be described if all three variables were in any one of the equations.



If there's a missing variable in a plane equation it's parallel to that axis, right?

skycat
1/12/2006, 04:46 PM
An equation that only has two variables describes a plane normal to an axis, right?

Rearrange your first equation and you get:

y=x-A

which is in the classic slope-intercept form for a linear equation with a slope of 1 and a y intercept of -A. Works for your other equations too. The number of variables determines the number of dimensions described by your equation.

yermom
1/12/2006, 04:48 PM
when i was messing around, i got 2 of the equations to equal each other, getting it down to 2 planes

x = z + B

y = z - C

yermom
1/12/2006, 04:50 PM
If there's a missing variable in a plane equation it's parallel to that axis, right?

yeah, that's why i was calling them planes

mdklatt
1/12/2006, 04:51 PM
Rearrange your first equation and you get:

y=x-A

which is in the classic slope-intercept form for a linear equation witha slope of 1 and a y intercept of -A. Works for your other equations too. The number of variables determines the number of dimensions described by your equation.

In three-space any number of variables (up to 3) denotes a plane. x = A is a plane, just like x - y = A and x - y - z = A.

Penguin
1/12/2006, 04:52 PM
Math is hard.

skycat
1/12/2006, 04:52 PM
eh, you guys are right. Sorry, I'm a doofus sometimes. Made a lot more sense to myself when comparing it to x=A in 2-space.

mdklatt
1/12/2006, 04:53 PM
n/m

GDC
1/12/2006, 04:57 PM
This is why I'm a biology major, even though I'm not a hippie or a lesbian. I topped out at calc 2.

yermom
1/12/2006, 04:59 PM
i should know this crap a lot better than i do... i was a math major at one point

i really should have made it to Linear Algebra more often

skycat
1/12/2006, 05:02 PM
Hell, I practically breathed vector algebra/calculus for a couple of years, and I made a really dumb mistake. I feel sharp as a tick right now.

mdklatt
1/12/2006, 05:07 PM
If you really want to feel inadequate try to pick up seismology in your spare time. Most meterology students have no idea how lucky they are that shear stress goes to zero in a fluid.

skycat
1/12/2006, 05:12 PM
If you really want to feel inadequate try to pick up seismology in your spare time. Most meterology students have no idea how lucky they are that shear stress goes to zero in a fluid.

Fluid dynamics was a weird course. Because all of the coupled sets of partial differential equations were too hard to solve, the course ended up being easier than courses where you could actually solve the equations.

mdklatt
1/12/2006, 05:15 PM
Fluid dynamics was a weird course. Because all of the coupled sets of partial differential equations were too hard to solve, the course ended up being easier than courses where you could actually solve the equations.


That's the beauty of atmospheric dynamics--all the really icky terms become insignificant once you do a scale analysis.

skycat
1/12/2006, 05:31 PM
OK, so I'm a beaten man. What's the equation of the line of intersection of those three (two) planes?

mdklatt
1/12/2006, 05:36 PM
OK, so I'm a beaten man. What's the equation of the line of intersection of those three (two) planes?

Beats me, I gave up on it.

yermom
1/12/2006, 05:45 PM
i kinda started doing the cross product of the normal vectors and decided i didn't care that much

Penguin
1/12/2006, 05:45 PM
OK, so I'm a beaten man. What's the equation of the line of intersection of those three (two) planes?

Pi equals exactly three.


You're welcome.

mdklatt
1/12/2006, 05:46 PM
i kinda started doing the cross product of the normal vectors and decided i didn't care that much


:D

critical_phil
1/12/2006, 05:49 PM
Pi equals exactly three.


You're welcome.

Australian Man Recites 4,400 Digit Number


By Associated Press

January 10, 2006, 4:36 PM EST

SYDNEY, Australia -- For Australian Chris Lyons, reciting a 4,400 digit number was as easy as pi. Lyons, 36, recited the first 4,400 digits of pi -- a mathematical value that has an infinite number of decimal places -- without a single error at the 2006 Mindsports Australia Festival on Monday, organizer David Cordover said Tuesday.

The memory coach from the southern city of Melbourne took 2 1/2 hours to complete the feat, Cordover said.

Lyons said he spent just one week memorizing the digits before reciting them for judges at the festival.

"With the right techniques and a bit of practice you can remember what ever you want," Lyons said.

Lyon's feat is far from the record, however.

In July, a Japanese psychiatric counselor recited pi to 83,431 decimal places from memory, breaking his own personal best of 54,000 digits and setting an unofficial world record, media reports said.
Copyright 2006 Newsday Inc.

mdklatt
1/12/2006, 05:54 PM
Australian Man Recites 4,400 Digit Number


This may be the most useless accomplishment in the history of mankind.

yermom
1/12/2006, 05:55 PM
you didn't read down far enough :D

mdklatt
1/12/2006, 05:57 PM
you didn't read down far enough :D

Yeah, I saw that--limitations of quoting a quote.

I would have been standing behind that guy whispering random numbers, like you do when somebody is trying to count something. :D

JohnnyMack
1/12/2006, 06:12 PM
I'm sorry guys, but this has to be done, it's for your own good.












































SNAP OUT OF IT!!!!!!!!!!!!!!!!
http://www.cinemaeye.com/images/uploads/dukes_video_02.jpg

skycat
1/12/2006, 06:15 PM
Well, I think I figured it out. It's just been too damn long since I'd done this. The equation for the line in vector notation is:

r = (0, -C-B, -B) + t(1,1,1)

In cartesian space it's:

x=y+C+B=z+B

And yes, I do feel better about myself. :O

Edit: fixed sign error.

skycat
1/12/2006, 06:17 PM
I just wanted to say that even my wife has no idea how dorky I truly am. I swear I can pass for (mostly) normal.

mdklatt
1/12/2006, 06:17 PM
SNAP OUT OF IT!!!!!!!!!!!!!!!!


You can just go and divide yourself by zero.

mdklatt
1/12/2006, 06:18 PM
Well, I think I figured it out. It's just been too damn long since I'd done this. The equation for the line in vector notation is:

r = (0, C-B, -B) + t(1,1,1)

In cartesian space it's:

x=y-C+B=z+B

And yes, I do feel better about myself. :O

Shouldn't A be in there somewhere?

skycat
1/12/2006, 06:20 PM
Shouldn't A be in there somewhere?

I think yermom got it right in that A=B+C, so it sort of is.