Results 1 to 3 of 3

Thread: vector multiplication: cross product

  1. Jan 29th, 2004, 05:05 PM #1
    udit99
    udit99 is offline

    Thread Starter
    Addicted Member
    Join Date
    Aug 2001
    Location
    India
    Posts
    203

    vector multiplication: cross product

    For any 3 given vectors : a,b,c the following Cross Product property should hold true :

    ax(bxc) = (axb)xc

    buit doesnt ...

    assuming
    a=(2,3,4)
    b=(1,2,3)
    c=(4,1,2)

    By the determinant method ,
    If I compute ax(bxc)= -61x + 18y +17z

    but

    (axb)xc = -5x+2y+9z

    ????
    Reply With Quote Reply With Quote
  2. Jan 30th, 2004, 05:39 PM #2
    TheManWhoCan
    TheManWhoCan is offline
    Lively Member
    Join Date
    Oct 2003
    Location
    Guildford, UK
    Posts
    91
    That could be because:

    a x (b x c) /= (a x b) x c

    That applies to a dot-product but not a cross product, since

    a x b = - b x a
    Reply With Quote Reply With Quote
  3. Jan 31st, 2004, 06:03 AM #3
    kedaman
    kedaman is offline
    transcendental analytic kedaman's Avatar
    Join Date
    Mar 2000
    Location
    0x002F2EA8
    Posts
    7,221
    the dot product is commutattive but can't be associative since it gives a scalar, but yeah the cross product is neither.
    Use
    writing software in C++ is like driving rivets into steel beam with a toothpick.
    writing haskell makes your life easier:
    reverse (p (6*9)) where p x|x==0=""|True=chr (48+z): p y where (y,z)=divMod x 13
    To throw away OOP for low level languages is myopia, to keep OOP is hyperopia. To throw away OOP for a high level language is insight.
    Reply With Quote Reply With Quote
« Previous Thread | Next Thread »

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Forum Rules


Click Here to Expand Forum to Full Width