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What does c-number stand for?

  1. Mar 18, 2005 #1
    I came across the word "c-number" several times. At first I thought it was an abbreviation of "complex number", but I found it is not true.

    One book says 3D dirac delta function evaluated at zero vector is an infinite c-number. What does it mean???
     
  2. jcsd
  3. Mar 18, 2005 #2
    c is normally constant, lightspeed (celeritas), complex number...

    marlon
     
  4. Mar 18, 2005 #3

    Chronos

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    Yikes. What does that infer about alphabetically challenged letters like g and h?
     
  5. Mar 18, 2005 #4

    arildno

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    The poor letters, I feel sorry for them; h needs a crutch in the form of a bar in order to be useful for physicists..
     
  6. Mar 18, 2005 #5

    Chronos

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    You are beyond my help, arildno :rofl:
     
  7. Mar 18, 2005 #6
    In which field is your c-number in? C-number is used in computational analysis to denote the number of basic steps needed to perform an algorithm or calculation.
     
  8. Mar 18, 2005 #7

    hellfire

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    Yes, I read something similar in Peskin & Schröder's "Introduction to QFT". I think this is an old nomenclature used by Dirac to distinguish between real or complex numbers (c-numbers or classical numbers) and operators (q-numbers or quantum numbers) in quantum mechanics.
     
  9. Sep 12, 2011 #8
    Just following up ... I came across the same thing in a book on quantum optics. In this context at least, the c-number is the classical number corresponding to a quantity (position, say) and the q-number (quantum number) is the corresponding operator for that quantity i.e. for position: x is the c-number for \hat{x}. I think it was used mainly for comparing classical and quantum pictures of the same variable with respect to the correspondence principle but I don't think many people use it anymore.
     
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