NAG Library Function Document

nag_rand_2_way_table (g05pzc)

void	nag_rand_2_way_table (Nag_ModeRNG mode, Integer nrow, Integer ncol, const Integer totr[], const Integer totc[], double r[], Integer lr, Integer state[], Integer x[], Integer pdx, NagError *fail)

3 Description

Given

m

row totals

R_{i}

and

n

column totals

C_{j}

(with

\sum_{i = 1}^{m} R_{i} = \sum_{j = 1}^{n} C_{j} = T

, say), nag_rand_2_way_table (g05pzc) will generate a pseudorandom two-way table of integers such that the row and column totals are satisfied.

The method used is based on that described by Patefield (1981) which is most efficient when

T

is large relative to the number of table entries

m \times n

(i.e.,

T > 2 m n

). Entries are generated one row at a time and one entry at a time within a row. Each entry is generated using the conditional probability distribution for that entry given the entries in the previous rows and the previous entries in the same row.

A reference vector is used to store computed values that can be reused in the generation of new tables with the same row and column totals. nag_rand_2_way_table (g05pzc) can be called to simply set up the reference vector, or to generate a two-way table using a reference vector set up in a previous call, or it can combine both functions in a single call.

One of the initialization functions nag_rand_init_repeatable (g05kfc) (for a repeatable sequence if computed sequentially) or nag_rand_init_nonrepeatable (g05kgc) (for a non-repeatable sequence) must be called prior to the first call to nag_rand_2_way_table (g05pzc).

4 References

Patefield W M (1981) An efficient method of generating

R \times C

tables with given row and column totals Appl. Stats. 30 91–97

5 Arguments

1: mode – Nag_ModeRNGInput

On entry: a code for selecting the operation to be performed by the function.

$mode = Nag_InitializeReference$: Set up reference vector only.
$mode = Nag_GenerateFromReference$: Generate two-way table using reference vector set up in a prior call to nag_rand_2_way_table (g05pzc).
$mode = Nag_InitializeAndGenerate$: Set up reference vector and generate two-way table.

Constraint:

mode = Nag_InitializeReference

Nag_GenerateFromReference

Nag_InitializeAndGenerate

2: nrow – IntegerInput

On entry:

m

, the number of rows in the table.

Constraint:

nrow \geq 2

3: ncol – IntegerInput

On entry:

n

, the number of columns in the table.

Constraint:

ncol \geq 2

4: totr[nrow] – const IntegerInput

On entry: the

m

row totals,

R_{i}

, for

i = 1, 2, \dots, m

Constraints:

$totr [i - 1] \geq 0$ , for $i = 1, 2, \dots, m$ ;
$\sum_{i = 1}^{m} totr [i - 1] = \sum_{j = 1}^{n} totc [j - 1]$ ;
$\sum_{i} totr [i - 1] > 0$ , for $i = 1, 2, \dots, m$ .

5: totc[ncol] – const IntegerInput

On entry: the

n

column totals,

C_{j}

, for

j = 1, 2, \dots, n

Constraints:

$totc [j - 1] \geq 0$ , for $j = 1, 2, \dots, n$ ;
$\sum_{j = 1}^{n} totc [j - 1] = \sum_{i = 1}^{m} totr [i - 1]$ .

6: r[lr] – doubleCommunication Array

On entry: if

mode = Nag_GenerateFromReference

, the reference vector from the previous call to nag_rand_2_way_table (g05pzc).

On exit: the reference vector.

7: lr – IntegerInput

On entry: the dimension of the array r.

Constraint:

lr \geq \sum_{i = 1}^{m} totr [i - 1] + 5

8: state[ $\dim$ ] – IntegerCommunication Array

Note: the dimension,

\dim

, of this array is dictated by the requirements of associated functions that must have been previously called. This array MUST be the same array passed as argument state in the previous call to nag_rand_init_repeatable (g05kfc) or nag_rand_init_nonrepeatable (g05kgc).

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

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

9: x[ $nrow \times pdx$ ] – IntegerOutput

On exit: if

mode = Nag_GenerateFromReference

Nag_InitializeAndGenerate

, a pseudorandom two-way

m

n

table,

X

, with element

x [(i - 1) \times pdx + j - 1]

containing the

(i, j)

th entry in the table such that

\sum_{i = 1}^{m} x [(i - 1) \times pdx + j - 1] = totc [j - 1]

and

\sum_{j = 1}^{n} x [(i - 1) \times pdx + j - 1] = totr [i - 1]

10: pdx – IntegerInput

On entry: the stride separating matrix column elements in the array x.

Constraint:

pdx \geq ncol

11: fail – NagError *Input/Output

The NAG error argument (see Section 3.6 in the Essential Introduction).

6 Error Indicators and Warnings

NE_ALLOC_FAIL: Dynamic memory allocation failed.
NE_BAD_PARAM: On entry, argument $⟨value⟩$ had an illegal value.
NE_INT: On entry, lr is not large enough, $lr = ⟨value⟩$ : minimum length required $= ⟨value⟩$ .
On entry, $ncol = ⟨value⟩$ .
Constraint: $ncol \geq 2$ .
On entry, $nrow = ⟨value⟩$ .
Constraint: $nrow \geq 2$ .
NE_INT_2: On entry, $pdx = ⟨value⟩$ and $ncol = ⟨value⟩$ .
Constraint: $pdx \geq ncol$ .
NE_INT_ARRAY: On entry, at least one element of totr is negative or totr sums to zero.
On entry, totc has at least one negative element.
NE_INT_ARRAY_2: On entry, the arrays totr and totc do not sum to the same total: totr array total is $⟨value⟩$ , totc array total is $⟨value⟩$ .
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.
NE_INVALID_STATE: On entry, state vector has been corrupted or not initialized.
NE_PREV_CALL: nrow or ncol is not the same as when r was set up in a previous call.
Previous value of $nrow = ⟨value⟩$ and $nrow = ⟨value⟩$ .
Previous value of $ncol = ⟨value⟩$ and $ncol = ⟨value⟩$ .

7 Accuracy

None.

8 Parallelism and Performance

Not applicable.

9 Further Comments

None.

10 Example

Following initialization of the pseudorandom number generator by a call to nag_rand_init_repeatable (g05kfc), this example generates and prints a

4

3

two-way table, with row totals of

9

11

7

and

23

respectively, and column totals of

16

17

and

17

respectively.

10.1 Program Text

Program Text (g05pzce.c)

10.2 Program Data

None.

10.3 Program Results

Program Results (g05pzce.r)

nag_rand_2_way_table (g05pzc) (PDF version)

g05 Chapter Contents

g05 Chapter Introduction

NAG Library Manual

NAG Library Function Documentnag_rand_2_way_table (g05pzc)

+− 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 Library Function Document

nag_rand_2_way_table (g05pzc)