| Re: Generating N random numbers that add to a TOTAL [message #89233 is a reply to message #89228] |
Thu, 07 August 2014 07:08   |
Russell Ryan
Messages: 122
Registered: May 2012
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Senior Member |
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On Wednesday, August 6, 2014 11:52:47 PM UTC-4, Gianguido Cianci wrote:
> Hi all,
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> I am wondering if anybody has suggestions on how to improve the function below. It seems ok for floating precision numbers.
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> For integers it's a different story:
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> It works great if N<<TOTAL. When N approaches TOTAL I get a few numbers and then a bunch of zeros... Also, setting /DIFFERENT makes it run for ever if N is large. Also, the sum of res adds up TOTAL=/-1, not always to TOTAL exactly...
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> Suggestions?
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> Thanks,
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> Gianguido
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> FUNCTION nrndaddto, n, total, integers = integers, different = different
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> compile_opt idl2
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> res = dblarr(n)
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> res[0] = randomu(seed, 1, /double)*(total)
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> FOR i = 1, n-2 DO BEGIN
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> res[i] = randomu(seed, 1, /double)*(total-total(res[0:i-1], /double))
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> ENDFOR
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> res[n-1] = total-total(res[0:n-2], /double)
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> IF ~keyword_set(integers) THEN integers = 0
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> IF keyword_set(integers) THEN res = round(res)
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> IF keyword_set(different) THEN BEGIN
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> IF n_elements(res) NE n_elements(unique(res, /sort)) THEN res = $
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> nrndaddto(n, total, integers = integers, different = 1)
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> ENDIF
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> RETURN, res
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> END
I should've said. Since the running total is converging to the requested total, the numbers are getting smaller with time. That is almost certainly related to why your sequence doesn't seem uniform.
R
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