[PHP] Random Number Problem

[litewarez]

Clocked it bitches:

Test Case:

$up = $down = 0;
while(true)
{
   if(abs((rand()%150)-50) < 50)
   {
      $up++;
   }else
   {
      $down++;
   }
   if( ($up + $down) == 1000){ break;} //500 loops for the test case
}

echo $up . '/' . $down; 

This gives results where the lower number is more likley.

run it keep refreshing and it will tell you the chances of the lower over the higher number.

So what you actually want is

$number = abs((rand()%150)-50); // 0-100 

[Hyperz]

Not the best implementation of what your friend suggest (I do suck at math) but this should work. As you generate more number the chance of getting a bigger number will increase.

// Setup
$min = 10;
$max = 1000;
$step = 0;
$index = 0;
$matrix = array();

// curve
for ($i = 0; $i < $max; $i++)
{
    $matrix[i] = $min + $step;
    
    if ($i & 1 && ($min + $step) < $max)
    {
        $step = ($step + 3 > $max - $min) $max - $min : $step + 3;
    }
}

// generate the next random number
function GetNext()
{
    return ($index < count($matrix)) ? rand(1, $matrix[$index++]) : rand(1, $matrix[$index]);
} 

This actually needs a class but I'm sure that's no problem for you . (didn't test it btw)

[litewarez]

Don't work dood, just returns 1 constantly.

// Setup
$min = 10;
$max = 1000;
$step = 0;
$index = 0;
$matrix = array();

// curve
for ($i = 0; $i < $max; $i++)
{
    $matrix[$i] = $min + $step; //Fix i to $i
    
    if ($i & 1 && ($min + $step) < $max)
    {
        $step = (($step + 3) > ($max - $min)) ? ($max - $min) : ($step + 3); //Wraped calculations
    }
}

// generate the next random number
function GetNext()
{
    return ($index < count($matrix)) ? rand(1, $matrix[$index++]) : rand(1, $matrix[$index]);
}  
echo GetNext(); //Returns 1 

-

Just thought of another way to do it!

$perecntage = 70; //70% to lower side

$direction = (rand(0,100) < $percentage /  ? 'lower' : 'hither'); //The chances of 0 - 100 is 70%
$number = ($direction == 'lower' ? rand(0,$percentage) : /*higher*/ rand($percentage,100)); 

This would work to get less than 70 most of the time 70%.

[Hyperz]

Don't wrap my calculations and expect to live .
Anyway, fixed the obvious:

<?php

$min = 10;
$max = 1000;
$step = 0;
$index = 0;
$matrix = array();

for ($i = 0; $i < $max; $i++)
{
    $matrix[$i] = $min + $step;
    
    if ($i & 1 && ($min + $step) < $max)
    {
        $step = ($step + 3 > $max - $min) ? $max - $min : $step + 3;
    }
}

function GetNext()
{
    global $matrix, $index;
    return ($index < count($matrix)) ? rand(1, $matrix[$index++]) : rand(1, $matrix[$index]);
}

?>

PS: PHP is shyte.

Edit:
Your other way doesn't do what he wants it to do.

[litewarez]

yea i know, the first one does using abs.

erm for some reason yours just keeps bringing back an average of 5, 1,8,9,7,8,7,9... it never gets higher then 10 and for a max of 1K it should do.

erm

function getRand()
{
    $check = rand(0,100);
    if($check < 70) //This means that 50% of the time, the below line will execute.
    {
        $check = rand(0,50);
        //Because the chances of the above being true are 70/100, this will execute.
        //And If it does not get to here then the $check will be within 70-100.
    }
}

echo getRand(); //Test. 

But i still think my other one is good aswell.

[Hyperz]

Well obviously if you keep refreshing it'll stay at a low number since the matrix and index gets rebuild every time. Put GetNext() in a for loop with 1000 irritations and you'll see it does exactly what it's supposed to do. Also, your methods aren't doing what he wants it to do. Otherwise my 1st example could be used which is still the fastest.

[jayfella]

i win. face it

[Mr Happy]

Well obviously if you keep refreshing it'll stay at a low number since the matrix and index gets rebuild every time. Put GetNext() in a for loop with 1000 irritations and you'll see it does exactly what it's supposed to do. Also, your methods aren't doing what he wants it to do. Otherwise my 1st example could be used which is still the fastest.

lol that's why it wasn't working for me either. I don't understand it but when it's put in a loop it does seam to work as it's meant to. Correct me if I'm wrong as I don't understand matrix but doesn't this mean that you have to run all 1000 and pick one of the 1000 at random to then get a result?

By the way for the original purpose it's not critical that this is worked out fully but I am finding it a huge learning experience which is probably more important.

@litewarez. That % thing is nice. Not exactly what I was after but I like how you did it.

[litewarez]

Well lets walk threw it:

abs() is a function used to set teh Absolute value of something, so that the number is not a negative but always a positive.

rand() with no parameters creates a number from 0 to the highest available number for that operating system.

the % is an Arithmetic Modulus operator what it does is return the remainder of A devided by B.

and the -50 you know.

heres a visual example.

$rand = 1045676;
$mod = ($rand % 150); //basically, how many times 150 goes into 1045676 and return the remainder.
//$mod is 26

$mod = $mod-50; // -24, but after abs() becomes 24; witch is a positive

//And all together
$number = abs(  (  rand()  %  150  )  -50  );; 

Hope this helps dood, its a sexy and small way

Do i win ??

[Hyperz]

lol that's why it wasn't working for me either. I don't understand it but when it's put in a loop it does seam to work as it's meant to. Correct me if I'm wrong as I don't understand matrix but doesn't this mean that you have to run all 1000 and pick one of the 1000 at random to then get a result?

By the way for the original purpose it's not critical that this is worked out fully but I am finding it a huge learning experience which is probably more important.

@litewarez. That % thing is nice. Not exactly what I was after but I like how you did it.

Maybe you should explain again what you want it to do. I thought you wanted to generate a random numbers that with each generated number have a higher probability of generating a bigger value. Since your friend suggested a matrix with a curve etc.