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PHP Challenges: Check whether a sequence of numbers is a geometric progression or not

PHP Challenges - 1: Exercise-16 with Solution

Write a PHP program to check whether a sequence of numbers is a geometric progression or not.

Input : array(2, 6, 18, 54)

In mathematics, a geometric progression or geometric sequence, is a sequence of numbers where each term after the first is found by multiplying the previous one by a fixed, non-zero number called the common ratio. For example, the sequence 2, 6, 18, 54, ... is a geometric progression with common ratio 3. Similarly, 10, 5, 2.5, 1.25, ... is a geometric sequence with common ratio 1/2.

Explanation :

PHP: Check whether a sequence of numbers is a geometric progression or not

Sample Solution :

PHP Code :

<?php
function is_geometric($arr)
{
    if (sizeof($arr) <= 1)
        return True;
    # Calculate ratio
    $ratio = $arr[1]/$arr[0];
   
    # Check the ratio of the remaining
    for($i=1; $i<sizeof($arr); $i++)
    {
        if (($arr[$i]/($arr[$i-1])) != $ratio)
        {
            return "Not a geometric sequence";
        }
    }        
  return "Geometric  sequence";
}
$my_arr1 = array(2, 6, 18, 54);
$my_arr2 = array(10, 5, 2.5, 1.20);

print_r(is_geometric($my_arr1)."\n");
print_r(is_geometric($my_arr2)."\n");
?>

Sample Output: 

Geometric  sequence                                         
Not a geometric sequence

Flowchart:

PHP Flowchart: Check whether a sequence of numbers is a geometric progression or not

PHP Code Editor:

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Previous: Write a PHP program to check whether a sequence of numbers is an arithmetic progression or not.
Next: Write a PHP program to compute the sum of the two reversed numbers and display the sum in reversed form.

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PHP: Tips of the Day

How to Sort Multi-dimensional Array by Value?

Try a usort, If you are still on PHP 5.2 or earlier, you'll have to define a sorting function first:

Example:

function sortByOrder($a, $b) {
    return $a['order'] - $b['order'];
}

usort($myArray, 'sortByOrder');

Starting in PHP 5.3, you can use an anonymous function:

usort($myArray, function($a, $b) {
    return $a['order'] - $b['order'];
});

And finally with PHP 7 you can use the spaceship operator:

usort($myArray, function($a, $b) {
    return $a['order'] <=> $b['order'];
});

To extend this to multi-dimensional sorting, reference the second/third sorting elements if the first is zero - best explained below. You can also use this for sorting on sub-elements.

usort($myArray, function($a, $b) {
    $retval = $a['order'] <=> $b['order'];
    if ($retval == 0) {
        $retval = $a['suborder'] <=> $b['suborder'];
        if ($retval == 0) {
            $retval = $a['details']['subsuborder'] <=> $b['details']['subsuborder'];
        }
    }
    return $retval;
});

If you need to retain key associations, use uasort() - see comparison of array sorting functions in the manual

Ref : https://bit.ly/3i77vCC