How to resolve the algorithm Sudan function step by step in the Julia programming language

Published on 22 June 2024 08:30 PM

How to resolve the algorithm Sudan function step by step in the Julia programming language

Table of Contents

Problem Statement

The Sudan function is a classic example of a recursive function, notable especially because it is not a primitive recursive function. This is also true of the better-known Ackermann function. The Sudan function was the first function having this property to be published. The Sudan function is usually defined as follows (svg):

F

0

( x , y )

= x + y

F

n + 1

( x , 0 )

= x

if

n ≥ 0

F

n + 1

( x , y + 1 )

=

F

n

(

F

n + 1

( x , y ) ,

F

n + 1

( x , y ) + y + 1 )

if

n ≥ 0

{\displaystyle {\begin{array}{lll}F_{0}(x,y)&=x+y\F_{n+1}(x,0)&=x&{\text{if }}n\geq 0\F_{n+1}(x,y+1)&=F_{n}(F_{n+1}(x,y),F_{n+1}(x,y)+y+1)&{\text{if }}n\geq 0\\end{array}}}

Write a function which returns the value of F(x, y).

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Sudan function step by step in the Julia programming language

The provided Julia code implements the Sudano function, which calculates a value based on three input integers (n, x, and y) using a recursive definition. It also uses the Memoize package to optimize the function's performance by caching previously calculated results. Here's a detailed explanation of the code:

  1. Loading the Memoize Package:

    using Memoize

    This line imports the Memoize package, which provides a macro (@memoize) to memoize functions, improving their performance by storing and reusing previously calculated results.

  2. Defining the sudan Function:

    @memoize function sudan(n, x, y)
      return n == 0 ? x + y : y == 0 ? x : sudan(n - 1, sudan(n, x, y - 1), sudan(n, x, y - 1) + y)
    end

    This function takes three integer arguments (n, x, and y) and computes a value based on the following logic:

    • If n is equal to 0, it returns the sum of x and y.
    • If y is equal to 0, it returns x.
    • Otherwise, it calculates sudan(n - 1, sudan(n, x, y - 1), sudan(n, x, y - 1) + y).

    The @memoize macro wraps the sudan function to memoize its results. When the sudan function is called with the same arguments multiple times, it will return the cached result instead of recalculating it, which can significantly improve performance, especially for recursive functions with many repeated calculations.

  3. Using the foreach Macro:

    foreach(t -> println("sudan($(t[1]), $(t[2]), $(t[3])) = ",
    sudan(t[1], t[2], t[3])), ((0,0,0), (1,1,1), (2,1,1), (3,1,1), (2,2,1)))

    The code uses the foreach macro to iterate over a sequence of tuples and perform a specific action for each tuple.

    • The sequence of tuples is defined as ((0,0,0), (1,1,1), (2,1,1), (3,1,1), (2,2,1)).

    • For each tuple t, the code prints a string of the form sudan(t[1], t[2], t[3]) = followed by the result of calling sudan(t[1], t[2], t[3]). So, it prints the value of the sudan function for the given input tuples.

By using the Memoize package to memoize the sudan function, the code can calculate and print the results efficiently, even for larger input values of n, as the function will not have to recompute previously calculated values.

Source code in the julia programming language

using Memoize

@memoize function sudan(n, x, y)
   return n == 0 ? x + y : y == 0 ? x : sudan(n - 1, sudan(n, x, y - 1), sudan(n, x, y - 1) + y)
end

foreach(t -> println("sudan($(t[1]), $(t[2]), $(t[3])) = ",
   sudan(t[1], t[2], t[3])), ((0,0,0), (1,1,1), (2,1,1), (3,1,1), (2,2,1)))


  

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