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Are vector spaces spans?

  1. Mar 17, 2009 #1
    Hello, very new to vector spaces, it seems like they take some getting used
    to. Anyway, since spans are sets of all the linear combinations of vectors
    contained within subspaces, I wonder whether or not vector spaces
    which contain elements (or vectors) that follow the ten axioms can be
    considered spans.
  2. jcsd
  3. Mar 17, 2009 #2
    You seem to be mixed up in your terminology.

    "Span" by itself doesn't really mean anything. You always talk about the span of a set of vectors.

    The span of a set of vectors is the set of all vectors that can be made from linear combinations of those vectors. This is the definition. It is easy to prove that a span of a set of vectors is a linear space itself.

    I'm not sure what "ten axioms" you're talking about.
  4. Mar 17, 2009 #3
    Oh so it doesn't just apply to subspaces. Yeah those ten axioms are
    rules that determine whether or not a set of vectors are contained
    within a vector space such as wheter or not they are closd under
    addition. Thank you for the response, very informative!:smile:
  5. Mar 17, 2009 #4
    I believe that you are refering to these ten:


    1. u + v is in V. (Closure under addition)
    2. u + v = v + u (Commutative property)
    3. u + (v + w) = (u + v) + w (Associative property)
    4. V has a zero vector 0 such that for every u in V, u = 0 = u (Additive identity)
    5. For every u in V, there is a vector in V denoted by -u such that u + (-u) = 0 (Additive inverse)

    Scalar Multiplication
    6. cu is in V. (Closure under scalar multiplication)
    7. c(u + v) = cu + cv (Distributive Property)
    8. (c + d)u= cu + du (Distributive Property)
    9. c(du) = (cd) u (Associative Property)
    10. 1(u) = u (Scalar Identity)

    ^From Elementary Linear Algebra by Larson, Edwards, and Falvo 5th edition.
  6. Mar 17, 2009 #5
    Yes, every vector space has a basis, i.e. a set of linearly independent vectors such that every element of the vector space is a linear combination of the set of basis vectors. This is true also for infinite dimensional vector spaces. There always exists a so-called Hamel basis which is a set of vectors such that every element of the vector space is a finite linear combination of the basis vectors.
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