g05 Chapter Contents
g05 Chapter Introduction
NAG C Library Manual

# NAG Library Function Documentnag_rngs_uniform (g05lgc)

## 1  Purpose

nag_rngs_uniform (g05lgc) generates a vector of pseudorandom numbers uniformly distributed over the interval $\left[a,b\right]$.

## 2  Specification

 #include #include
 void nag_rngs_uniform (double a, double b, Integer n, double x[], Integer igen, Integer iseed[], NagError *fail)

## 3  Description

If $a=0$ and $b=1$, nag_rngs_uniform (g05lgc) returns the next $n$ values ${y}_{i}$ from a uniform $\left(0,1\right)$ generator (see nag_rngs_basic (g05kac) for details).
For other values of $a$ and $b$, nag_rngs_uniform (g05lgc) applies the transformation
 $xi=a+b-ayi.$
The function ensures that the values ${x}_{i}$ lie in the closed interval $\left[a,b\right]$.
If computing sequentially and using the same generator, nag_rngs_uniform (g05lgc) always generates exactly the same pseudorandom numbers as would $n$ consecutive calls of nag_rngs_basic (g05kac) and on many machines is likely to be much faster.
One of the initialization functions nag_rngs_init_repeatable (g05kbc) (for a repeatable sequence if computed sequentially) or nag_rngs_init_nonrepeatable (g05kcc) (for a non-repeatable sequence) must be called prior to the first call to nag_rngs_uniform (g05lgc).

## 4  References

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

## 5  Arguments

2:     bdoubleInput
On entry: the end points $a$ and $b$ of the uniform distribution.
Constraint: ${\mathbf{a}}\le {\mathbf{b}}$.
3:     nIntegerInput
On entry: $n$, the number of pseudorandom numbers to be generated.
Constraint: ${\mathbf{n}}\ge 0$.
4:     x[n]doubleOutput
On exit: the $n$ pseudorandom numbers from the specified uniform distribution.
5:     igenIntegerInput
On entry: must contain the identification number for the generator to be used to return a pseudorandom number and should remain unchanged following initialization by a prior call to nag_rngs_init_repeatable (g05kbc) or nag_rngs_init_nonrepeatable (g05kcc).
6:     iseed[$4$]IntegerCommunication Array
On entry: contains values which define the current state of the selected generator.
On exit: contains updated values defining the new state of the selected generator.
7:     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_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_REAL_2
On entry, ${\mathbf{a}}=〈\mathit{\text{value}}〉$ and ${\mathbf{b}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{b}}\ge {\mathbf{a}}$.

Not applicable.

None.

## 9  Example

This example prints five pseudorandom numbers from a uniform distribution between $-1.0$ and $1.0$, generated by a single call to nag_rngs_uniform (g05lgc), after initialization by nag_rngs_init_repeatable (g05kbc).

### 9.1  Program Text

Program Text (g05lgce.c)

None.

### 9.3  Program Results

Program Results (g05lgce.r)