# NAG CL Interfaceg05kgc (init_​nonrepeat)

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## 1Purpose

g05kgc initializes the selected base generator to generate a non-repeatable sequence of variates. The base generator can then be used by the group of pseudorandom number functions (see g05khcg05kjc, g05ncc, g05ndc, g05pdcg05pjc, g05pxcg05pzc, g05rcc, g05rdc, g05ryc, g05rzc and g05sacg05tlc) and the quasi-random scrambled sequence initialization function, g05ync.

## 2Specification

 #include
 void g05kgc (Nag_BaseRNG genid, Integer subid, Integer state[], Integer *lstate, NagError *fail)
The function may be called by the names: g05kgc, nag_rand_init_nonrepeat or nag_rand_init_nonrepeatable.

## 3Description

g05kgc selects a base generator through the input value of the arguments genid and subid, and then initializes it based on the values taken from the real-time clock, resulting in the same base generator yielding different sequences of random numbers each time the calling program is run. It should be noted that there is no guarantee of statistical properties between sequences, only within sequences.
A definition of some of the terms used in this description, along with details of the various base generators can be found in the G05 Chapter Introduction.

## 4References

L'Ecuyer P and Simard R (2002) TestU01: a software library in ANSI C for empirical testing of random number generators Departement d'Informatique et de Recherche Operationnelle, Universite de Montreal https://www.iro.umontreal.ca/~lecuyer
Maclaren N M (1989) The generation of multiple independent sequences of pseudorandom numbers Appl. Statist. 38 351–359
Matsumoto M and Nishimura T (1998) Mersenne twister: a 623-dimensionally equidistributed uniform pseudorandom number generator ACM Transactions on Modelling and Computer Simulations
Wichmann B A and Hill I D (2006) Generating good pseudo-random numbers Computational Statistics and Data Analysis 51 1614–1622
Wikramaratna R S (1989) ACORN - a new method for generating sequences of uniformly distributed pseudo-random numbers Journal of Computational Physics 83 16–31

## 5Arguments

1: $\mathbf{genid}$Nag_BaseRNG Input
On entry: must contain the type of base generator to use.
${\mathbf{genid}}=\mathrm{Nag_Basic}$
NAG basic generator.
${\mathbf{genid}}=\mathrm{Nag_WichmannHill_I}$
Wichmann Hill I generator.
${\mathbf{genid}}=\mathrm{Nag_MersenneTwister}$
Mersenne Twister.
${\mathbf{genid}}=\mathrm{Nag_WichmannHill_II}$
Wichmann Hill II generator.
${\mathbf{genid}}=\mathrm{Nag_ACORN}$
ACORN generator.
${\mathbf{genid}}=\mathrm{Nag_MRG32k3a}$
L'Ecuyer MRG32k3a generator.
See the G05 Chapter Introduction for details of each of the base generators.
Constraint: ${\mathbf{genid}}=\mathrm{Nag_Basic}$, $\mathrm{Nag_WichmannHill_I}$, $\mathrm{Nag_MersenneTwister}$, $\mathrm{Nag_WichmannHill_II}$, $\mathrm{Nag_ACORN}$ or $\mathrm{Nag_MRG32k3a}$.
2: $\mathbf{subid}$Integer Input
On entry: if ${\mathbf{genid}}=\mathrm{Nag_WichmannHill_I}$, subid indicates which of the $273$ sub-generators to use. In this case, the sub-generator is used.
If ${\mathbf{genid}}=\mathrm{Nag_ACORN}$, subid indicates the values of $k$ and $p$ to use, where $k$ is the order of the generator, and $p$ controls the size of the modulus, $M$, with $M={2}^{\left(p×30\right)}$. If ${\mathbf{subid}}<1$, the default values of $k=10$ and $p=2$ are used, otherwise values for $k$ and $p$ are calculated from the formula, ${\mathbf{subid}}=k+1000\left(p-1\right)$.
If ${\mathbf{genid}}=\mathrm{Nag_MRG32k3a}$ and the range of the generator is set to $\left(0,1\right]$, otherwise the range is set to $\left(0,1\right)$; in this case the sequence is identical to the implementation of MRG32k3a in TestU01 (see L'Ecuyer and Simard (2002)) for identical seeds.
For all other values of genid, subid is not referenced.
3: $\mathbf{state}\left[{\mathbf{lstate}}\right]$Integer Communication Array
On exit: contains information on the selected base generator and its current state. If ${\mathbf{lstate}}<1$ then state may be NULL.
4: $\mathbf{lstate}$Integer * Input/Output
On entry: the dimension of the state array, or a value $<1$. If the Mersenne Twister (${\mathbf{genid}}=\mathrm{Nag_MersenneTwister}$) is being used and the skip ahead function g05kjc or g05kkc will be called subsequently, then you must ensure that ${\mathbf{lstate}}\ge 1260$.
On exit: if ${\mathbf{lstate}}<1$ on entry, then the required length of the state array for the chosen base generator, otherwise lstate is unchanged. When ${\mathbf{genid}}=\mathrm{Nag_MersenneTwister}$ (Mersenne Twister) a value of $1260$ is returned, allowing for the skip ahead function to be subsequently called. In all other cases the minimum length, as documented in the constraints below, is returned.
Constraints:
• if ${\mathbf{genid}}=\mathrm{Nag_Basic}$, ${\mathbf{lstate}}\ge 17$;
• if ${\mathbf{genid}}=\mathrm{Nag_WichmannHill_I}$, ${\mathbf{lstate}}\ge 21$;
• if ${\mathbf{genid}}=\mathrm{Nag_MersenneTwister}$, ${\mathbf{lstate}}\ge 633$;
• if ${\mathbf{genid}}=\mathrm{Nag_WichmannHill_II}$, ${\mathbf{lstate}}\ge 29$;
• if ${\mathbf{genid}}=\mathrm{Nag_ACORN}$, ${\mathbf{lstate}}\ge \mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(\left(k+1\right)×p+9,14\right)+3$, where $k$ and $p$ are defined by subid;
• if ${\mathbf{genid}}=\mathrm{Nag_MRG32k3a}$, ${\mathbf{lstate}}\ge 61$;
• otherwise ${\mathbf{lstate}}<1$.
5: $\mathbf{fail}$NagError * Input/Output
The NAG error argument (see Section 7 in the Introduction to the NAG Library CL Interface).

## 6Error Indicators and Warnings

NE_ALLOC_FAIL
Dynamic memory allocation failed.
See Section 3.1.2 in the Introduction to the NAG Library CL Interface for further information.
On entry, argument $⟨\mathit{\text{value}}⟩$ had an illegal value.
NE_INT
On entry, ${\mathbf{lstate}}=⟨\mathit{\text{value}}⟩$.
Constraint: ${\mathbf{lstate}}\le 0$ or ${\mathbf{lstate}}\ge ⟨\mathit{\text{value}}⟩$.
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 contact NAG for assistance.
See Section 7.5 in the Introduction to the NAG Library CL Interface for further information.
NE_NO_LICENCE
Your licence key may have expired or may not have been installed correctly.
See Section 8 in the Introduction to the NAG Library CL Interface for further information.

Not applicable.

## 8Parallelism and Performance

g05kgc is not threaded in any implementation.

None.

## 10Example

In order to preserve the statistical properties of the base generators, g05kgc should only be called once. If multiple streams of values are required then one of the methods described in Section 2.1.1 in the G05 Chapter Introduction should be used.
However, for illustrative purposes only, this example calls g05kgc twice. At each call a sample of $500$ values from a discrete uniform distribution are generated and then the two samples are compared.

### 10.1Program Text

Program Text (g05kgce.c)

None.

### 10.3Program Results

Program Results (g05kgce.r)