Mean

Discrete uniform distribution expected value.

The expected value for a discrete uniform random variable is

where a is the minimum support and b the maximum support of the distribution.

Usage

var mean = require( '@stdlib/stats/base/dists/discrete-uniform/mean' );

mean( a, b )

Returns the expected value of a discrete uniform distribution with parameters a (minimum support) and b (maximum support).

var v = mean( 0, 1 );
// returns 0.5

v = mean( 4, 12 );
// returns 8.0

v = mean( 2, 8 );
// returns 5.0

If a or b is not an integer value, the function returns NaN.

var v = mean( 0.1, 2 );
// returns NaN

v = mean( 0, 2.2 );
// returns NaN

v = mean( NaN, 2 );
// returns NaN

v = mean( 2, NaN );
// returns NaN

If provided a > b, the function returns NaN.

var y = mean( 3, 2 );
// returns NaN

y = mean( -1, -2 );
// returns NaN

Examples

var randu = require( '@stdlib/random/base/randu' );
var round = require( '@stdlib/math/base/special/round' );
var mean = require( '@stdlib/stats/base/dists/discrete-uniform/mean' );

var a;
var b;
var v;
var i;

for ( i = 0; i < 10; i++ ) {
    a = round( randu()*10.0 );
    b = round( ( randu()*10.0 ) + a );
    v = mean( a, b );
    console.log( 'a: %d, b: %d, E(X;a,b): %d', a.toFixed( 4 ), b.toFixed( 4 ), v.toFixed( 4 ) );
}

C APIs

Usage

#include "stdlib/stats/base/dists/discrete-uniform/mean.h"

stdlib_base_dists_discrete_uniform_mean( a, b )

Returns the expected value of a discrete uniform distribution with parameters a (minimum support) and b (maximum support).

double out = stdlib_base_dists_discrete_uniform_mean( 0, 1 );
// returns 0.5

The function accepts the following arguments:

a: [in] int32_t minimum support.
b: [in] int32_t maximum support.

double stdlib_base_dists_discrete_uniform_mean( const int32_t a, const int32_t b );

Examples

#include "stdlib/stats/base/dists/discrete-uniform/mean.h"
#include "stdlib/math/base/special/round.h"
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>

static double random_uniform( const double min, const double max ) {
    double v = (double)rand() / ( (double)RAND_MAX + 1.0 );
    return min + ( v*(max-min) );
}

int main( void ) {
    int32_t a;
    int32_t b;
    double y;
    int i;

    for ( i = 0; i < 10; i++ ) {
        a = stdlib_base_round( random_uniform( 0.0, 10.0 ) );
        b = stdlib_base_round( random_uniform( 0.0, 10.0 ) ) + a;
        y = stdlib_base_dists_discrete_uniform_mean( a, b );
        printf( "a: %d, b: %d, E(X;a,b): %lf\n", a, b, y );
    }
}