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  21 
  22 Strength Reduction
  23 ------------------
  24 
  25 Strength reduction replaces an expansive operation by a cheaper one, such as
  26 multiplication by addition or subtraction, multiplication instead of
  27 exponentiation; use compound assignment operators such as += wherever possible,
  28 changing code of the form a[i] = a[i] + x to a[i] += x, since they result in
  29 fewer bytecode instructions; use shifts instead of multiplication by powers of
  30 two, etc.
  31 
  32 For example:
  33 
  34         x ** 2  = x * x
  35         2.0 * x = x + x
  36         x / 2   = x * 0.5
  37 
  38 
  39 Induction Variable
  40 ------------------
  41 
  42 A variable is called an induction variables of a loop if every time the variable
  43 changes values it is incremented or decrmented by some constant.
  44 Basic induction variables i whose only assignments within the loop is of the
  45 form i += c, where c is a constant.