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In computer programming, an infinite loop (or endless loop) [1] [2] is a sequence of instructions that, as written, will continue endlessly, unless an external intervention occurs, such as turning off power via a switch or pulling a plug. It may be intentional.
A loop invariant is an assertion which must be true before the first loop iteration and remain true after each iteration. This implies that when a loop terminates correctly, both the exit condition and the loop invariant are satisfied. Loop invariants are used to monitor specific properties of a loop during successive iterations.
A generator expression may be used in Python versions >= 2.4 which gives lazy evaluation over its input, and can be used with generators to iterate over 'infinite' input such as the count generator function which returns successive integers:
However, infinite loops can sometimes be used purposely, often with an exit from the loop built into the loop implementation for every computer language, but many share the same basic structure and/or concept. The While loop and the For loop are the two most common types of conditional loops in most programming languages.
Python 2.5 implements better support for coroutine-like functionality, based on extended generators Python 3.3 improves this ability, by supporting delegating to a subgenerator ( PEP 380 ) Python 3.4 introduces a comprehensive asynchronous I/O framework as standardized in PEP 3156 , which includes coroutines that leverage subgenerator delegation
Introduced in Python 2.2 as an optional feature and finalized in version 2.3, generators are Python's mechanism for lazy evaluation of a function that would otherwise return a space-prohibitive or computationally intensive list. This is an example to lazily generate the prime numbers:
The achievable H ∞ norm of the closed loop system is mainly given through the matrix D 11 (when the system P is given in the form (A, B 1, B 2, C 1, C 2, D 11, D 12, D 22, D 21)). There are several ways to come to an H ∞ controller: A Youla-Kucera parametrization of the closed loop often leads to very high-order controller.
The highlighted assertions within the loop body, at the beginning and end of the loop (lines 6 and 11), are exactly the same. They thus describe an invariant property of the loop. When line 13 is reached, this invariant still holds, and it is known that the loop condition i!=n from line 5 has become false.