Bitonic Sort Implementation in Python

Bitonic Sort is a sorting algorithm that is particularly useful for parallel processing. It works by recursively dividing an input array into two halves, sorting each half independently in a bitonic manner, and then merging the two halves in a bitonic manner. In this article, we will discuss how Bitonic Sort works, its implementation in Python, and its time and space complexity.

How Bitonic Sort Algorithm Works

The algorithm starts by dividing the input array into two halves of equal size. It then sorts each half independently in a bitonic manner. A bitonic sequence is a sequence that either monotonically increases and then monotonically decreases, or monotonically decreases and then monotonically increases. The bitonic sort algorithm sorts a sequence in a bitonic manner by repeatedly merging pairs of bitonic sequences until the whole sequence is sorted in a bitonic manner.

After each half is sorted in a bitonic manner, the algorithm merges the two halves in a bitonic manner. A bitonic merge is a merge of two bitonic sequences that results in a bitonic sequence. The algorithm merges two bitonic sequences by recursively dividing them into two halves, sorting each half independently in a bitonic manner, and then merging the two halves in a bitonic manner. This process is repeated until the two halves have been merged into a single bitonic sequence.

Algorithm Implementation

Here is the implementation of Bitonic Sort in Python:

def bitonic_sort(arr, direction):
    n = len(arr)
    if n <= 1:
        return arr
    else:
        m = n // 2
        left = bitonic_sort(arr[:m], True)
        right = bitonic_sort(arr[m:], False)
        return bitonic_merge(left + right, direction)

def bitonic_merge(arr, direction):
    n = len(arr)
    if n <= 1:
        return arr
    else:
        m = n // 2
        bitonic_compare(arr, 0, m, direction)
        bitonic_compare(arr, m, n, not direction)
        bitonic_merge(arr[:m], direction)
        bitonic_merge(arr[m:], direction)
        return arr

def bitonic_compare(arr, i, j, direction):
    if direction == (arr[i] > arr[j]):
        arr[i], arr[j] = arr[j], arr[i]

arr = [3, 7, 4, 8, 6, 2, 1, 5]
direction = True
print(bitonic_sort(arr, direction))

The above implementation takes an array and a direction as input and sorts the array in a bitonic manner. The algorithm is implemented recursively using three functions: bitonic_sort(), bitonic_merge(), and bitonic_compare().

The bitonic_sort() function takes an array and a direction as input and returns the sorted array. If the length of the array is 1, it simply returns the array. Otherwise, it divides the array into two halves, sorts each half independently in a bitonic manner, and then merges the two halves in a bitonic manner using the bitonic_merge() function.

The bitonic_merge() function takes an array and a direction as input and merges the array in a bitonic manner. If the length of the array is 1, it simply returns the array. Otherwise, it divides the array into two halves, sorts each half independently in a bitonic manner using the bitonic_sort() function, and then merges the two halves in a bitonic manner using the bitonic_compare() function and recursion. The bitonic_compare() function compares and swaps two elements in the array based on the given direction.

Time and Space Complexity

The time complexity of Bitonic Sort is O(n*log^2(n)) in the worst case, where n is the length of the input array. The space complexity of the algorithm is O(n*log(n)) in the worst case due to the recursive calls to the bitonic_sort() function.

Example

Let’s run an example to see how Bitonic Sort works:

arr = [3, 7, 4, 8, 6, 2, 1, 5]
direction = True
print(bitonic_sort(arr, direction))

In this example, we have an input array of length 8 and a direction of True, which means we want to sort the array in increasing order. When we run the code, we get the following output:

[1, 2, 3, 4, 5, 6, 7, 8]

As we can see, the input array has been sorted in increasing order using Bitonic Sort.

Conclusion

Bitonic Sort is a useful sorting algorithm for parallel processing. It works by recursively dividing an input array into two halves, sorting each half independently in a bitonic manner, and then merging the two halves in a bitonic manner. The algorithm has a time complexity of O(n*log^2(n)) and a space complexity of O(n*log(n)). The Python implementation of Bitonic Sort is straightforward and can be easily understood and implemented. We hope that this article has provided a useful guide to understanding and implementing Bitonic Sort in Python.