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2 edition of weaker precondition for loops. found in the catalog.

weaker precondition for loops.

H J. Boom

weaker precondition for loops.

by H J. Boom

  • 188 Want to read
  • 11 Currently reading

Published by Mathematisch Centrum in Amsterdam .
Written in English


Edition Notes

SeriesIW 104/78
ContributionsMathematisch Centrum. Afdeling Informatica.
ID Numbers
Open LibraryOL13743342M

specification, it must be the case that whenever the precondition is satisfied initially, the postcondition is also satisfied when the algorithm finishes. Theorem SimpleSelect meets the specification given in Figure Proof: First, we assume that the precondition for SimpleSelect(A[n]). HTTP has a concept of conditional requests, where the result, and even the success of a request, can be changed by comparing the affected resources with the value of a validator. Such requests can be useful to validate the content of a cache, and sparing a useless control, to verify the integrity of a document, like when resuming a download, or when preventing to lose updates when uploading or.

Our goal is to carry out some simple examples of program verification-- i.e., to use the precise definition of Imp to prove formally that particular programs satisfy particular specifications of their 'll develop a reasoning system called Floyd-Hoare Logic-- often shortened to just Hoare Logic-- in which each of the syntactic constructs of Imp is equipped with a generic "proof rule. One of the examples should be the small program in the book’s preface which, specialised to p =1/3, becomes a program for making a fair three-way choice using a two-sided coin: x:= 1/3; WHILE 1/2 DO // Choose w/prob 1/2 whether to (re)enter or exit the loop.

The Loop book. Read reviews from the world's largest community for readers. Helen Ross is a year-old biologist, sent into a hostile place to prote /5(). It seems a lot of things done in practice relax weakest precondition for loops to a precondition that is suitable for verification. The above from wikipedia suggests that given a loop invariant, one can indeed compute the weakest preconditions on the nose, but I am having trouble understanding this condition.


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Weaker precondition for loops by H J. Boom Download PDF EPUB FB2

A Weaker Precondition for Loops A Weaker Precondition for Loops Boom, H. A Weaker Precondition for Loops H. BOOM Concordia University In his book, A Discipline of Programming, Dijkstra presents the skeleton for a programming language and defines its semantics axiomatically using weaker precondition for loops.

book transformers. HIS language involves only bounded nondeterminism. Predicate transformer semantics were introduced by Edsger Dijkstra in his seminal paper "Guarded commands, nondeterminacy and formal derivation of programs".They define the semantics of an imperative programming paradigm by assigning to each statement in this language a corresponding predicate transformer: a total function between two predicates on the state space of the statement.

Weakest-Precondition Reasoning lReference: ra, A Discipline of Programming, Prentice-Hall, lStarting with a post-assertion, what is the weakest pre-condition that makes the assertion true.

lIn other words, what must be true before to make the assertion true after. l[WP ^ [test&action] ] → Assertion What do we mean by “weakest”.

So, to strengthen a condition is to replace it with a stronger one; to weaken a condition is to replace it with a weaker on. Because a condition is always stronger and weaker than itself, the phrase "strengthen the precondition and weaken the postcondition" does indeed mean that we can leave one (or even both!) of them unchanged.

To find the weakest precondition we take t = 3 x + 1 7, such that p [u ∖ t] evaluates to 3 x + 1 7 5 x and x > 8. For the application in relaxed metric planning, assume that an assignment of the form h ← e x p is subject to a postcondition e x p ′.

The weakest precondition of it is established by substituting the occurrence of h in e x. Loops Definition Loops are constructions, that allow us to execute one or several actions multiple times.

They consists of two major parts: a truth condition and a body. The body contains the actions that we want to repeat. Each execution of the body block is called iteration. The condition decides whether the iterations will continue or not. Well-founded induction and the invariance theorem for loops.

Author links open overlay panel Joseph M. Morris. Show more. The precondition tells us that all of the haystack elements up to and including the element at index i are not the needle. You can use induction to prove that the precondition is true every time the program reaches it.

The loop ends when its condition is false, which means the first postcondition is true. TL;DR. The OODA loop was a tool developed by military strategist John Boyd to explain how individuals and organizations can win in uncertain and chaotic environments.

It is an Acronym that explains the four steps of decisions making: Observe, Orient, Decide Act. This article will give you the understanding you need to turn ambiguity into advantage and risk into results in your career.

for (precondition,what has to be true to continue,postcopndition) {// sumething} so first before he enters a loop he do the precondition. than chek the 2 thing. and then enters the loop. after he does the post condition. here is an example of for. for (int i=1,i.

Precondition definition is - prerequisite. How to use precondition in a sentence. Recent Examples on the Web: Noun Calvinism, in other words, was less capitalism’s cause than its ironic precondition.

— George Blaustein, The New Republic, "Searching for Consolation in Max Weber’s Work Ethic," 2 July Governor Abbott in Texas has said the precondition for opening the economy is wearing. A weaker precondition for loops, Math. Centrum Report, Amsterdam, Google Scholar [EL85] Emerson, E.A., Chin-Laung Lei, Modalities for Model Checking: Branching Time Logic Strikes Back, POPL Buy Physical Book Learn about institutional subscriptions.

Cite paper. A precondition is something that must be true before some section of code; and a postcondition, after. The "Requires" clause above in the documentation of random_int is a kind of precondition.

It says that the client of the random_int function is responsible for guaranteeing something about the value of bound. • Books and developers already informally speak about read and write sets • Can be efficiently discharged using current compiler technology: – Memory dependence analysis – Alias/pointer analysis – Loop analysis – Range analysis – Weakest Precondition Synthesis for Compiler Optimizations Language of Preconditions: Suitability.

A Weaker Precondition for Loops Mathematisch Centrum Report IW /78, Google Scholar [6] Broy, M., Gratz, R. and Wirsing, M., Semantics of Non-Deterministic and Non-Continuous Constructs in Bauer, F.L. and Broy, M.

(eds.) Program Construction, International Summer School Markloberdorf, July Lecture Notes in Computer Science   Precondition of an operation is a condition that should be satisfied before the operation can be performed.

Postcondition of an operation is a condition that should be satisfied after the operation has been performed. So, let’s take some operation. Intuition Example 3 ctd. In fact Q(y + z) is the weakest precondition. Intuitive justification: Let v be the value arrived at by computing x:=y+z. If Q(x) is true after the assignment, so is Q(v).

If Q(v) is true after the assignment, then it must also be true before the assignment, because x does not appear in Q(v) and nothing else has changed. Thus, Q(y + z) was true initially. Judy's precondition for success, in finding a mate, was a red herring.

But first things first. Before tackeling her procrastination, we needed to rule out a hoarding compulsion. This video explains the concept of a counted loop in programming and then gives an example program in both pseudocode and as a mind map.

a for-loop that probably uses the method’s parameter variables, an if statement, probably inside the loop, a call to other class methods given to you, a numerical or string value that is calculated by the loop and returned at the end of the method. if the question has 2 parts, 1 part will probably require a loop and the other just an expression.

Infinite loops \LOOP \ENDLOOP Precondition \REQUIRE Postcondition \ENSURE Returning variables \RETURN Printing variables \PRINT Note: Due to a bug, the algorithmic package is not compatible with hyperref. Also in this section.The precondition for this does not lie in associating superior and inferior, but in the total victory of the former.

The stronger must dominate and not blend with the weaker, thus sacrificing his own greatness. Only the born weakling can view this as cruel, but he after all is only a weak and limited man; for if this law did not prevail, any.while-loops •So no objects or methods for now • This lecture: The idea, without loops, in 3 passes 1.

High-level intuition of forward and backward reasoning 2. Precise definition of logical assertions, preconditions, etc. 3. Definition of weaker/stronger and weakest-precondition • Next lecture: Loops UW CSE Winter 7.