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Taking only the positive sqrt in Mathematica

  1. May 27, 2010 #1
    As my title says, I need to take only the positive square root of some evaluation. For my calculation, the negative square root is extraneous.

    What I do is a normalization of a wave function:

    Code (Text):
    J = Integrate[Psi[x]^2, {x, 0, a}]
    sol = Solve[J == 1, A]
    A /. sol
     
    My only problem is those above expression will give me A = {-1/sqrt(2), 1/sqrt(2)}.

    How can I force Mathematica to only give me positive square root?
     
  2. jcsd
  3. May 27, 2010 #2
    Code (Text):
    DeleteCases[A,x_/;x<0]
    This will ofc only work with expressions mathematica can evaluate numerically or knows to be positive or negative.
     
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