difference equation
A relation between consecutive elements of a sequence. The first difference is
 
 	D u(n) = u(n+1) - u(n)
 where u(n) is the nth element of sequence u. The second difference is
 	D2 u(n) = D (D u(n))
		= (u(n+2) - u(n+1)) - (u(n+1) - u(n))
		= u(n+2) - 2u(n+1) + u(n)
 And so on. A recurrence relation such as
 	u(n+2) + a u(n+1) + b u(n) = 0
 can be converted to a difference equation (in this case, a second order 
							linear difference equation):
 	D2 u(n) + p D u(n) + q u(n) = 0
 and vice versa. a, b, p, q are constants.
(1995-02-10)
 
  
 
  
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