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How to calculate powers of a 2x2 matrix WITHOUT eigenvectors ?

  1. Apr 20, 2012 #1
    How do I determine powers of matrices(2x2) without calculating their eigenvectors and doing the pdp^-1 thing ?

    Obviously multiplying over and over is not a solution.
     
  2. jcsd
  3. Apr 20, 2012 #2
    I'll let someone else try doing that without straight multiplication, but even with straight multiplication, there is a way.

    If you want only one power, find its binary representation: b0+b1*2+b2*2^2+...

    Then calculate powers of the matrix: M^4 = (M^2)^ 2, M^8 = (M^4)^2, etc.
    Then assemble the final result: identity * (multiply by M if b0 is 1) * (multiply by M^2 if b1 is 1) * (multiply by M^4 if b2 is 1) * ...

    For power p, instead of p multiplications, one has to do around 2*log(2,p) ones.
     
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