Integer, Intent (In)	::	n, m, sorder, ldx, sdx
Integer, Intent (Inout)	::	state(*), ifail
Real (Kind=nag_wp), Intent (In)	::	theta
Real (Kind=nag_wp), Intent (Inout)	::	x(ldx,sdx)

C Header Interface

#include <nag.h>

void	g05rhf_ (const Integer n, const Integer m, const double theta, const Integer sorder, Integer state[], double x[], const Integer ldx, const Integer sdx, Integer *ifail)

The routine may be called by the names g05rhf or nagf_rand_copula_clayton.

3 Description

Generates

n

pseudorandom uniform

m

-variates whose joint distribution is the Clayton/Cook–Johnson Archimedean copula

C_{θ}

, given by

C_{θ} = {(u_{1}^{- θ} + u_{2}^{- θ} + \dots + u_{m}^{- θ} - m + 1)}^{- 1 / θ}, {\begin{matrix} θ \in (0, \infty), \\ u_{j} \in (0, 1], j = 1, \dots m; \end{matrix}

with the special case:

$C_{\infty} = \min (u_{1}, u_{2}, \dots, u_{m})$ , the Fréchet–Hoeffding upper bound.

The generation method uses mixture of powers.

One of the initialization routines g05kff (for a repeatable sequence if computed sequentially) or g05kgf (for a non-repeatable sequence) must be called prior to the first call to g05rhf.

4 References

Marshall A W and Olkin I (1988) Families of multivariate distributions Journal of the American Statistical Association 83 403

Nelsen R B (2006) An Introduction to Copulas (2nd Edition) Springer Series in Statistics

5 Arguments

1: $n$ – Integer Input

On entry:

n

, the number of pseudorandom uniform variates to generate.

Constraint:

n \geq 0

2: $m$ – Integer Input

On entry:

m

, the number of dimensions.

Constraint:

m \geq 2

3: $theta$ – Real (Kind=nag_wp) Input

On entry:

θ

, the copula parameter.

Constraint:

theta \geq 1.0 \times 10^{−6}

4: $sorder$ – Integer Input

On entry: determines the storage order of variates; the

(i, j)

th variate is stored in

x (i, j)

sorder = 1

, and

x (j, i)

sorder = 2

, for

i = 1, 2, \dots, n

and

j = 1, 2, \dots, m

Constraint:

sorder = 1

2

5: $state (*)$ – Integer array Communication Array

Note: the actual argument supplied must be the array state supplied to the initialization routines g05kff or g05kgf.

On entry: contains information on the selected base generator and its current state.

On exit: contains updated information on the state of the generator.

6: $x (ldx, sdx)$ – Real (Kind=nag_wp) array Output

On exit: the pseudorandom uniform variates with joint distribution described by

C_{θ}

, with

x (i, j)

holding the

i

th value for the

j

th dimension if

sorder = 1

and the

j

th value for the

i

th dimension of

sorder = 2

7: $ldx$ – Integer Input

On entry: the first dimension of the array x as declared in the (sub)program from which g05rhf is called.

Constraints:

if $sorder = 1$ , $ldx \geq n$ ;
if $sorder = 2$ , $ldx \geq m$ .

8: $sdx$ – Integer Input

On entry: the second dimension of the array x as declared in the (sub)program from which g05rhf is called.

Constraints:

if $sorder = 1$ , $sdx \geq m$ ;
if $sorder = 2$ , $sdx \geq n$ .

9: $ifail$ – Integer Input/Output

On entry: ifail must be set to

0

−1

1

to set behaviour on detection of an error; these values have no effect when no error is detected.

A value of

0

causes the printing of an error message and program execution will be halted; otherwise program execution continues. A value of

−1

means that an error message is printed while a value of

1

means that it is not.

If halting is not appropriate, the value

−1

1

is recommended. If message printing is undesirable, then the value

1

is recommended. Otherwise, the value

0

is recommended. When the value $- 1$ or $1$ is used it is essential to test the value of ifail on exit.

On exit:

ifail = 0

unless the routine detects an error or a warning has been flagged (see Section 6).

6 Error Indicators and Warnings

If on entry

ifail = 0

−1

, explanatory error messages are output on the current error message unit (as defined by x04aaf).

Errors or warnings detected by the routine:

$ifail = 1$: On entry, corrupt state argument.

$ifail = 2$: On entry, invalid theta: $theta = ⟨ value ⟩$ .
Constraint: $theta \geq 1.0 \times 10^{−6}$ .

$ifail = 3$: On entry, $n = ⟨ value ⟩$ .
Constraint: $n \geq 0$ .

$ifail = 4$: On entry, $m = ⟨ value ⟩$ .
Constraint: $m \geq 2$ .

$ifail = 5$: On entry, invalid sorder.
Constraint: $sorder = 1$ or $2$ .

$ifail = 7$: On entry, ldx must be at least $⟨ value ⟩$ : $ldx = ⟨ value ⟩$ .

$ifail = 8$: On entry, sdx must be at least $⟨ value ⟩$ : $sdx = ⟨ value ⟩$ .

$ifail = - 99$: An unexpected error has been triggered by this routine. Please contact NAG.
See Section 7 in the Introduction to the NAG Library FL Interface for further information.

$ifail = - 399$: Your licence key may have expired or may not have been installed correctly.
See Section 8 in the Introduction to the NAG Library FL Interface for further information.

$ifail = - 999$: Dynamic memory allocation failed.
See Section 9 in the Introduction to the NAG Library FL Interface for further information.

7 Accuracy

Not applicable.

8 Parallelism and Performance

Background information to multithreading can be found in the Multithreading documentation.

g05rhf is threaded by NAG for parallel execution in multithreaded implementations of the NAG Library.

Please consult the X06 Chapter Introduction for information on how to control and interrogate the OpenMP environment used within this routine. Please also consult the Users' Note for your implementation for any additional implementation-specific information.

9 Further Comments

In practice, the need for numerical stability restricts the range of

θ

such that:

the routine requires $θ \geq 1.0 \times 10^{−6}$ ;
if $θ > 200.0$ , the routine returns pseudorandom uniform variates with $C_{\infty}$ joint distribution.

10 Example

This example generates thirteen four-dimensional variates for copula

C_{1.3}

g05rh: FL CL CPP AD PY MB

NAG FL Interfaceg05rhf (copula_​clayton)

▸▿ Contents

1 Purpose

2 Specification

3 Description

4 References

5 Arguments

6 Error Indicators and Warnings

7 Accuracy

8 Parallelism and Performance

9 Further Comments

10 Example

10.1 Program Text

10.2 Program Data

10.3 Program Results

NAG FL Interface
g05rhf (copula_clayton)