This code is supposed to generate a sequence of 10,000 random numbers in VBA. For some reason I am only able to produce a unique sequence of length 5842, and then it repeats. But, and this is the strangest part, each time I run the code, the sequence starts in a different place. For example in one run, the elements following element 2660 are the same as those following element 8502 (8502-2660= 5842). The next run, I get a sequence that repeats following elements 3704 and 9546 (9546-3704=5842). And so on.
Function NormRand() As Double
' NormRand returns a randomly distributed drawing from a
' standard normal distribution i.e. one with:
' Average = 0 and Standard Deviation = 1.0
Dim fac As Double, rsq As Double, v1 As Double, v2 As Double
Static flag As Boolean, gset As Double
' Each pass through the calculation of the routine produces
' two normally-distributed deviates, so we only need to do
' the calculations every other call. So we set the flag
' variable (to true) if gset contains a spare NormRand value.
If flag Then
NormRand = gset
' Force calculation next time.
flag = False
Else
' Don't have anything saved so need to find a pair of values
' First generate a co-ordinate pair within the unit circle:
Do
v1 = 2 * Rnd - 1#
v2 = 2 * Rnd - 1#
rsq = v1 * v1 + v2 * v2
Loop Until rsq <= 1#
' Do the Math:
fac = Sqr(-2# * Log(rsq) / rsq)
' Return one of the values and save the other (gset) for next time:
NormRand = v2 * fac
gset = v1 * fac
flag = True
End If
End Function
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