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Another example of inductive definition is the natural numbers (or positive integers): A natural number is either 1 or n+1, where n is a natural number. Similarly recursive definitions are often used to model the structure of expressions and statements in programming languages.
Many mathematical axioms are based upon recursive rules. For example, the formal definition of the natural numbers by the Peano axioms can be described as: "Zero is a natural number, and each natural number has a successor, which is also a natural number." [2] By this base case and recursive rule, one can generate the set of all natural numbers.
Constant functions : For each natural number and every , the k-ary constant function, defined by (, …,) = , is primitive recursive.; Successor function: The 1-ary successor function S, which returns the successor of its argument (see Peano postulates), that is, () = +, is primitive recursive.
The nth partial sum is given by a simple formula: = = (+). This equation was known to the Pythagoreans as early as the sixth century BCE. [5] Numbers of this form are called triangular numbers, because they can be arranged as an equilateral triangle.
The subset sum problem (SSP) is a decision problem in computer science. In its most general formulation, there is a multiset of integers and a target-sum , and the question is to decide whether any subset of the integers sum to precisely . [1] The problem is known to be NP-complete.
Another example is a similar singly linked type in Java: class List < E > { E value ; List < E > next ; } This indicates that non-empty list of type E contains a data member of type E, and a reference to another List object for the rest of the list (or a null reference to indicate that this is the end of the list).
The μ-recursive functions (or general recursive functions) are partial functions that take finite tuples of natural numbers and return a single natural number.They are the smallest class of partial functions that includes the initial functions and is closed under composition, primitive recursion, and the minimization operator μ.
The recursion theorem states that such a definition indeed defines a function that is unique. The proof uses mathematical induction. [1] An inductive definition of a set describes the elements in a set in terms of other elements in the set. For example, one definition of the set of natural numbers is: