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

Dot Product Calculator Quandry

  1. Jan 16, 2006 #1
    I'm going nuts here and I can't figure this out. I have two complex vectors:
    A=(1+i)x + (1)y +(i)z
    B=(4-i)x +(0)y + (2-2i)z
    If I do the dot product of these on my calculator I get 1 + 7i, however when I do this by hand I keep getting 7 +5i. What am I doing wrong? When figuring this out by hand I am going by the assumption that AB=AxBx + AyBy + AzBz.
  2. jcsd
  3. Jan 16, 2006 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Are you using parentheses properly?
  4. Jan 16, 2006 #3
    I figured it out. I need to take the conjugate of the second vector. This is sure going to get confusing with Quantum Mechanics!
  5. Jan 17, 2006 #4


    User Avatar
    Science Advisor

    Yes that's correct, for a complex inner product you take the conjugate of the second argument. It's defined that way so that if you take the inner product of a vector with itself then you'll always end up with just a real number. This real number is called the "norm" and is a generalized measure of the length of the vector.
    Last edited: Jan 17, 2006
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook