Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Matrix algebra help

  1. Oct 25, 2011 #1
    Find X if

    X' * X =
    (50, 300)
    (300, 1000)

    Then find Y if
    Y * X =
    (300, 2000)

    Problem is that when I try to solve for X (or X') first, I get three equations with four unknowns (a11, a12, a21, a22). Any help?
     
  2. jcsd
  3. Oct 25, 2011 #2
    I'm not sure what your notation is. Does X' mean adjoint, transpose, or what? You should have 4 equations in 4 unknowns, however, since each entry of the resultant matrix is found by multiplying elements of the individual matrices (and there are 4 elements in the resultant matrix).
     
  4. Oct 25, 2011 #3
    Yes, the ' is transpose.

    I get
    a11 ^2 + a21 ^2 = 50
    a11 * a12 + a21 * a22 = 300
    a12 ^2 + a22 ^2 = 1000

    but I can't get the fourth equation?
     
  5. Oct 25, 2011 #4
    The matrix X must be 2 columns, but how many rows? Is X a simple 2x2 matrix?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook