Linear algebra!!!! :)

[ElDonAntonio]

Hey guys,

I posted this in off-topic but they seemed rather confused, I guess I'll find more knowledgeable people here 😉 😉

I have two vectors, say L and N, and I want to find a new vector that's a symmetry of L around N. Drawing to explain

ANyone remembers how to do that??? my textbooks are too dusty...
Thanks!
Antonio

 

[Shalmanese]

buh? are those meant to be 3d?

Oh wait, I get it. but sorry, mind too far gone to think properly 🙁.

 

[CTho9305]

i can do it if N is a vector along the line y=x, but thats all I can remember 😉

 

[Stealth1024]

What you want is N (the middle one) to be the resultant vector of of the component vectors L and W ("what I want"), considering that L and W are of equal magnitude.

There is a simple way to do this on paper or you can use equations we learned in physics class...

 

[Armitage]

<< Hey guys,

I posted this in off-topic but they seemed rather confused, I guess I'll find more knowledgeable people here 😉 😉

I have two vectors, say L and N, and I want to find a new vector that's a symmetry of L around N. Drawing to explain

ANyone remembers how to do that??? my textbooks are too dusty...
Thanks!
Antonio >>



Just find the angle between L and N and rotate it by twice that angle in the correct direction.
You can use the dot product to find the angle: L .dot. N = |L||N|cos(theta)

The vector rotation is:

L' = C L

where C = {{cos(alpha), sin(alpha)}, {sin(alpha), cos(alpha)}}

 

[Superdoopercooper]

I would just like to thank you...

I started to convulse when I read this thread... and got down to the L = C'L or whatever. < me shakes right now >

That was one of those classes I think I got 96% or higher on 3 out of the 5 quizzes, but still got a B in teh class, b/c class avg. was so high, and the midterm had all this totally useless and retarted row and column space crap that made no practical sense whatsoever.

< shakes again >

 

[RemyCanad]

umm ok...
I could tell you how to find the opposite of the two vectors combined. ie-- what vector would make them all = 0. But I dont know that symmetry of l around n means. 😛

 

[CSoup]

<< I would just like to thank you...

I started to convulse when I read this thread... and got down to the L = C'L or whatever. < me shakes right now >

That was one of those classes I think I got 96% or higher on 3 out of the 5 quizzes, but still got a B in teh class, b/c class avg. was so high, and the midterm had all this totally useless and retarted row and column space crap that made no practical sense whatsoever.

< shakes again > >>



yeah, same at Cornell. Many people who got around 100 percent on the prelims (tests) unexpectedly got B's in the class because since most people did so well during the semester that the grade ended up being determined by the final.