g05 Chapter Contents
g05 Chapter Introduction
NAG C Library Manual

NAG Library Function Documentnag_rand_discrete_uniform (g05tlc)

1  Purpose

nag_rand_discrete_uniform (g05tlc) generates a vector of pseudorandom integers uniformly distributed over the interval $\left[a,b\right]$.

2  Specification

 #include #include
 void nag_rand_discrete_uniform (Integer n, Integer a, Integer b, Integer state[], Integer x[], NagError *fail)

3  Description

nag_rand_discrete_uniform (g05tlc) generates the next $n$ values ${y}_{i}$ from a uniform $\left(0,1\right]$ generator (see nag_rand_basic (g05sac) for details) and applies the transformation
 $xi = a+ b-a+1 yi ,$
where $⌊z⌋$ is the integer part of the real value $z$. The function ensures that the values ${x}_{i}$ lie in the closed interval $\left[a,b\right]$.
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_discrete_uniform (g05tlc).

4  References

Knuth D E (1981) The Art of Computer Programming (Volume 2) (2nd Edition) Addison–Wesley

5  Arguments

1:     nIntegerInput
On entry: $n$, the number of pseudorandom numbers to be generated.
Constraint: ${\mathbf{n}}\ge 0$.
2:     aIntegerInput
3:     bIntegerInput
On entry: the end points $a$ and $b$ of the uniform distribution.
Constraint: ${\mathbf{a}}\le {\mathbf{b}}$.
4:     state[$\mathit{dim}$]IntegerCommunication Array
Note: the actual argument supplied must be the array state supplied to the initialization functions 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.
5:     x[n]IntegerOutput
On exit: the $n$ pseudorandom numbers from the specified uniform distribution.
6:     failNagError *Input/Output
The NAG error argument (see Section 3.6 in the Essential Introduction).

6  Error Indicators and Warnings

On entry, argument $〈\mathit{\text{value}}〉$ had an illegal value.
NE_INT
On entry, ${\mathbf{n}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{n}}\ge 0$.
NE_INT_2
On entry, ${\mathbf{a}}=〈\mathit{\text{value}}〉$ and ${\mathbf{b}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{b}}\ge {\mathbf{a}}$.
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.

Not applicable.

None.

9  Example

This example prints five pseudorandom integers from a discrete uniform distribution between $-5$ and $5$, generated by a single call to nag_rand_discrete_uniform (g05tlc), after initialization by nag_rand_init_repeatable (g05kfc).

9.1  Program Text

Program Text (g05tlce.c)

None.

9.3  Program Results

Program Results (g05tlce.r)