PHP, Structures and Functions, Fundamental Syntaxes

RANDOM NUMBERS

are numbers that occur in a sequence such that two conditions are met:

1 . the values are uniformly distributed over a defined interval or set.
2 . it is impossible to predict future values based on past or present ones.

Random numbers are important in statistical analysis and probability theory.

There is no need to use srand or mt_srand as this is done automatically when we need to seed the random number generator.

Since PHP 7.1.0, srand becames an alias of mt_srand .

Since PHP 7.1.0 mt_rand has been updated to use the fixed, correct, version of the Mersenne Twister Algorithm.

To fall back to the old behaviour, use mt_srand with MT_RAND_PHP as the second parameter.

This function uses the MTRNG, Mersenne Twister Random Number:

Mersenne Twister


<?php

void mt_srand ( int $seed = 0 , 
                         int $mode = MT_RAND_MT19937 )

where,

$seed = Arbitrary INTEGER value to be used as seed
            
$mode = CONSTANT to specify the implementation 
                 of the algorithm to be used
                    ( SEE the below TABLE )
            
?>

$seed

Arbitrary INTEGER value to be used as seed.

$mode

Use one of the following constants to specify the implementation of the algorithm to use:

CONSTANT	VALUE	DESCRIPTION
MT_RAND_MT19937	0	Uses the fixed, correct, Mersenne Twister implementation. Available as of PHP 7.1.0.
MT_RAND_PHP	1	Uses an incorrect Mersenne Twister implementation. Used as the default up till PHP 7.1.0. This mode is available for backward compatibility.
ed48

EXERCISE


<?php
 
$mtsrnd01  = mt_srand();

var_dump($mtsrnd01);

?>

RESULT

NULL

... is returned always.

EXERCISE


<?php

$seed02 = 100;

$mode = mt_rand(0, 1);
// MT_RAND_MT19937 = 0;
// MT_RAND_PHP = 1
 
$mtsrnd02  = mt_srand($seed02);

var_dump($mtsrnd02);

?>