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NAG[g05nbc] NAG[nag_rngs_sample] - Pseudo-random sample from an integer vector
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Calling Sequence
g05nbc(ipop, isampl, igen, iseed, 'n'=n, 'm'=m, 'fail'=fail)
nag_rngs_sample(. . .)
Parameters
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ipop - Vector(1..n, datatype=integer[kernelopts('wordsize')/8]);
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On entry: the population to be sampled.
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isampl - Vector(1..m, datatype=integer[kernelopts('wordsize')/8]);
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On exit: the selected sample.
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iseed - Vector(1.. , datatype=integer[kernelopts('wordsize')/8]);
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On entry: contains values which define the current state of the selected generator.
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On exit: contains updated values defining the new state of the selected generator.
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'n'=n - integer; (optional)
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On entry: the number of elements in the population vector to be sampled.
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Constraint:  . .
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'm'=m - integer; (optional)
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On entry: the sample size.
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Constraint:  . .
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'fail'=fail - table; (optional)
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The NAG error argument, see the documentation for NagError.
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Description
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Purpose
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nag_rngs_sample (g05nbc) selects a pseudo-random sample without replacement from an integer vector.
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Error Indicators and Warnings
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"NE_BAD_PARAM"
On entry, argument  had an illegal value.
"NE_INT"
On entry,  . Constraint:  .
"NE_INT_2"
On entry,  or  :  ,  .
"NE_INTERNAL_ERROR"
An internal error has occurred in this function. Check the function call and any array sizes. If the call is correct then please consult NAG for assistance.
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Further Comments
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The time taken by nag_rngs_sample (g05nbc) is of order  .
In order to sample other kinds of vectors, or matrices of higher dimension, the following technique may be used:
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a. set ![ipop[i] = i](/support/helpjp/helpview.aspx?si=9868/file08520/math206.png) , for  ;
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b. use nag_rngs_sample (g05nbc) to take a sample from ipop and put it into isampl;
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c. use the contents of isampl as a set of indices to access the relevant vector or matrix.
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In order to divide a population into several groups, g05nac (nag_rngs_permute) is more efficient.
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Examples
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n := 8:
m := 1:
igen := 1:
ipop := Vector([1, 2, 3, 4, 5, 6, 7, 8], datatype=integer[kernelopts('wordsize')/8]):
isampl := Vector(1, datatype=integer[kernelopts('wordsize')/8]):
iseed := Vector([1762543, 9324783, 1542344, 742355], datatype=integer[kernelopts('wordsize')/8]):
NAG:-g05nbc(ipop, isampl, igen, iseed, 'n' = n, 'm' = m):
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