Question

can any one tell that in vector space spanning set is the smallest subspace of vector space or not?

Answer 1

Im not exactly sure what you are asking. The smallest subspace is always 0

Answer 2

You may be wondering if a set of vectors that spans a vector space is the smallest number of vectors to form a basis then no think of a set of vectors that spans 2 space

(0,1) and (1,0) and (1,1)

This is will span R^2 but you dont "need (1,1) because it is linearly dependent of (0,1) and (1,0)

Answer 3

If this is what you are asking then take a look at contraction and expansion thms. These should lead you to the answer

Answer 4

actually my que is the part of a theorem
THEOREM:Let v1,v2,v3...,vn be vectors in a vector space V and let their span be W=span{v1,v2,....,vn} then,

(a) W is a subspace of V.

(b) W is the smallest subspace of V that contains all of the vectors .

and i want the proof of its 2nd part.
can u help me plz....

Answer 5

Yes I see what you are saying now. Try proof by contridiction. That is, assume that W is not the smallest subspace

Answer 6

i tried but do not get the point
plz u proof it if u can...

Answer 7

This proof is kind of tricky just because it is so trival.

Im not going to give you the answer but here is how i would go about the proof without using contridiciton.

If you wanted to make the smallest subspace you would just put in the vectors v1, .... , vn

Answer 8

but subspaces force you to be able to add and multiply any two vectors and remain in the subpsace

Answer 9

Therefore if you want a subspace with all of the vectors you must have the span of all of the vectors

Answer 10

Basically, say what the smallest subspace can be (just all of the vectors by themselfs) then say the def of a subspace forces the span of all of the vectors to be the smallest subspace

Answer 11

from all these how can u say w is SMALLEST subspace?

Answer 12

ok ok Ill do the proof :)

Answer 13

The smallest SET that contains v1, ....,vn is (v1,....vn)

Now is this SET a SUBSPACE?
no not nessarly can we take any vi and any vj and have vi + vj is an element of our SET

so we need to have any vi + vj to be in our SET and any constant,c, cvi to make it a SUBSPACE.

the span of v1,...,vn by def is a SET that contains v1,...,vn and any vi + vj and cvi so this span is the smallest SUBSPACE becasue it contains no more than v1,...,vn, and has closure under additon and scalar mutiplication

Answer 14

I uppercased set and subspace to make sure you didnt confuse them as you were reading it.

Answer 15

now the last part where i claim span(v1, ... vn) is the smallest should be ok for most poeple. if you want to be super rigourous then say, make the subspace any smaller and it will not contain every c*(vi + vj) and thus making it not a subspace

Answer 16

no not nessarly can we take any vi and any vj and have vi + vj NOT an element of our SET

Answer 17

thanks a lot. now i try to understand it

Answer 18

ok good! just remeber this...

start with the smallest set of v1,....vn
see if your set is a subspace
add enough vectors to make a subspace
show that if you take away any vectors you will lose closure under addition or multiplication