PHP, Mathematical Functions

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(0, 0);



var_dump($mtsrnd01);



?>

RESULT

NULL

... is returned

EXERCISE


<?php



$seed02 = 100;

$mode =  MT_RAND_PHP;

 

$mtsrnd02  = mt_srand($seed02);



var_dump($mtsrnd02);



?>

RESULT

NULL

... is returned

EXERCISE


<?php



$seed03 = 120;



$mode03 = 30;

 

$srd03  = mt_srand($seed03, $mode03);



var_dump($srd03);



?>