EVOLUTION-MANAGER

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<table width="100%" summary="page for Random.user {base}"><tr><td>Random.user {base}</td><td style="text-align: right;">R Documentation</td></tr></table>

<h2>User-supplied Random Number Generation</h2>

<h3>Description</h3>

<p>Function <code><a href="Random.html">RNGkind</a></code> allows user-coded uniform and
normal random number generators to be supplied.  The details are given
here.
</p>

<h3>Details</h3>

<p>A user-specified uniform RNG is called from entry points in
dynamically-loaded compiled code.  The user must supply the entry point
<code>user_unif_rand</code>, which takes no arguments and returns a
<em>pointer to</em> a double. The example below will show the general
pattern. The generator should have at least 25 bits of precision.
</p>
<p>Optionally, the user can supply the entry point <code>user_unif_init</code>,
which is called with an <code>unsigned int</code> argument when
<code><a href="Random.html">RNGkind</a></code> (or <code>set.seed</code>) is called, and is intended
to be used to initialize the user's RNG code.  The argument is intended
to be used to set the &lsquo;seeds&rsquo;; it is the <code>seed</code> argument to
<code>set.seed</code> or an essentially random seed if <code><a href="Random.html">RNGkind</a></code>
is called.
</p>
<p>If only these functions are supplied, no information about the
generator's state is recorded in <code>.Random.seed</code>.  Optionally,
functions <code>user_unif_nseed</code> and <code>user_unif_seedloc</code> can be
supplied which are called with no arguments and should return pointers
to the number of seeds and to an integer (specifically, <span class="samp">Int32</span>)
array of seeds.  Calls to <code>GetRNGstate</code> and <code>PutRNGstate</code>
will then copy this array to and from <code>.Random.seed</code>.
</p>
<p>A user-specified normal RNG is specified by a single entry point
<code>user_norm_rand</code>, which takes no arguments and returns a
<em>pointer to</em> a double.
</p>

<h3>Warning</h3>

<p>As with all compiled code, mis-specifying these
functions can crash <span style="font-family: Courier New, Courier; color: #666666;"><b>R</b></span>.  Do include the &lsquo;<span class="file">R_ext/Random.h</span>&rsquo;
header file for type checking.
</p>

<h3>Examples</h3>

<pre>## Not run: 
##  Marsaglia's congruential PRNG
#include &lt;R_ext/Random.h&gt;

static Int32 seed;
static double res;
static int nseed = 1;

double * user_unif_rand()
{
    seed = 69069 * seed + 1;
    res = seed * 2.32830643653869e-10;
    return &amp;res;
}

void  user_unif_init(Int32 seed_in) { seed = seed_in; }
int * user_unif_nseed() { return &amp;nseed; }
int * user_unif_seedloc() { return (int *) &amp;seed; }

/*  ratio-of-uniforms for normal  */
#include &lt;math.h&gt;
static double x;

double * user_norm_rand()
{
    double u, v, z;
    do {
        u = unif_rand();
        v = 0.857764 * (2. * unif_rand() - 1);
        x = v/u; z = 0.25 * x * x;
        if (z &lt; 1. - u) break;
        if (z &gt; 0.259/u + 0.35) continue;
    } while (z &gt; -log(u));
    return &amp;x;
}

## Use under Unix:
R CMD SHLIB urand.c
R
&gt; dyn.load("urand.so")
&gt; RNGkind("user")
&gt; runif(10)
&gt; .Random.seed
&gt; RNGkind(, "user")
&gt; rnorm(10)
&gt; RNGkind()
[1] "user-supplied" "user-supplied"

## End(Not run)</pre>

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