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 :

Sample Solution :

PHP Code :

<?php
// Function to check if an array forms a geometric sequence
function is_geometric($arr)
{
    // If the array has 1 or fewer elements, it's automatically considered a geometric sequence
    if (sizeof($arr) <= 1)
        return True;
    
    // Calculate the ratio between the second and first elements of the array
    $ratio = $arr[1] / $arr[0];
   
    // Check the ratio of the remaining elements
    for ($i = 1; $i < sizeof($arr); $i++)
    {
        // If the ratio of any pair of consecutive elements is not equal to the initial ratio, return "Not a geometric sequence"
        if (($arr[$i] / ($arr[$i - 1])) != $ratio)
        {
            return "Not a geometric sequence";
        }
    }        

    // If all ratios are equal, return "Geometric sequence"
    return "Geometric sequence";
}

// Define two arrays
$my_arr1 = array(2, 6, 18, 54);
$my_arr2 = array(10, 5, 2.5, 1.20);

// Test the is_geometric function with the defined arrays and print the results
print_r(is_geometric($my_arr1) . "\n");
print_r(is_geometric($my_arr2) . "\n");
?>

Explanation:

Here is a brief explanation of the above PHP code:

• Function definition:
• The code defines a function named "is_geometric()" which checks if an array forms a geometric sequence. It takes an array '$arr' as input.
• Inside the function:
• It first checks if the size of the array is 1 or less. If so, it returns 'True' as any sequence with 1 or fewer elements is considered geometric.
• It calculates the ratio between the second and first elements of the array.
• It iterates through the array elements starting from the second element.
• Within each iteration, it checks if the ratio of the current element to the previous element is equal to the initial ratio calculated.
• If any ratio is not equal to the initial ratio, it returns "Not a geometric sequence".
• If all ratios are equal, it returns "Geometric sequence".
• Function Call & Testing:
• Two arrays '$my_arr1' and '$my_arr2' are defined with different sets of numbers.
• The "is_geometric()" function is called twice with these arrays as input.
• Finally the results of the function calls are printed using "print_r()", which displays whether each input array forms a geometric sequence.

Sample Output:

Geometric  sequence                                         
Not a geometric sequence

Flowchart:

PHP Code Editor:

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