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X_tanspose*x vs. x*x_transpose

  1. Apr 17, 2009 #1
    x is a vector - (x1,x2, ..., xn)_transpose (i.e. a column vector). so when we have x_transpose*x we have x1^2+ x2^2+...+xn^2 = norm(x)^2.

    right...

    now what's x*x_transpose, i.e. column times the row? is it an n-by-n matrix?

    actually now that i'm finished typing it i'm pretty sure it is, but i'll still post it to be sure..
     
  2. jcsd
  3. Apr 17, 2009 #2
    What does your asterisk mean? Sometimes an asterisk means the complex conjugate of a transpose, but I'm not sure that's how you mean it here.
     
  4. Apr 17, 2009 #3
    * means "times" as in 2*2=4
     
  5. Apr 18, 2009 #4

    matt grime

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    The definition of matrix multiplication is that when you compose an i by j matrix with a j by k matrix you get an i by k matrix.
     
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