# Tagged Questions

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### I need help understanding how to prove partial correctness

Please help me understand how I would prove the partial correctness of the below pseudocode with respect to the following predicates: Pre: {n>=0} Post: ...
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### Finding a good loop invariant for a powering procedure

Consider the following algorithm for computing integer powers: ...
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### Proving correctness of a loop that calculates the sum of array

I am trying to mathematically prove that the following program is correct: ...
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### Does checking for correctness belong predominantly to “semantic analysis”?

Does checking for correctness belong predominantly to "semantic analysis"? Or is it reasonable to be done in earlier phases (in a compiler like construction) as well? Mainly in syntax analysis. Or is ...
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### Why precondition strengtening is sound in Hoare logic

I have problem with understanding why precondition strengthening is sound rule in Hoare logic. The rule is: $${P \implies Q, \{Q\} C \{X\} } \over {\{P\} C \{X\}}$$ I really do not understand why ...
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### Hoare logic - partial/total correctnes and strength invariant

I'm studying Hoare logic and I can't understand the relation between partial and total correctness regarding loop invariant. Suppose for example that I have the following program: ...
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### Global relabeling heuristic: Push-relabel maxflow

I have a correct, working implementation of the preflow-push-relabel maxflow algorithm [2]. I am trying to implement the global relabeling update heuristic [3], but have run into some issues. I have ...
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### Hoare Calculus Incorrect Assignment Axiom

I'm currently preparing for an exam and recently came across the following exercise and would like to know whether my solution would be correct. Exercise: Prove that the following axiom is not ...
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### Can we quantify how close a partially correct programs is to being correct?

I know that there is something called partial correctness, but I was wondering if there was a way to tell how close a semi-correct program is to a fully correct program. For example, if you had a ...
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### Could program verification techniques prevent bugs of the genre of Heartbleed from occurring?

On the matter of the Heartbleed bug, Bruce Schneier wrote in his Crypto-Gram of 15th April: '"Catastrophic" is the right word. On the scale of 1 to 10, this is an 11.' I read several years ago that a ...
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### Formal program verification in practice

As a software engineer, I write a lot of code for industrial products. Relatively complicated stuff with classes, threads, some design efforts, but also some compromises for performance. I do a lot of ...
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### Proof of Program Correctness - Loop Invariants

I've been reading a book on using loop invariants and induction to prove program correctness. Then I came across the following program which got me thinking... Specification for ...
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### Does this loop invariant guarantee that the variable never changes?

Suppose you have some loop and and integer k: int k = 5; for (int i = 0 ; i < N; i++) { //(*) //do something } The loop invariant at (*) is: $\{ K=k\}$ ...
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### Loop Invariants as Tautologies

Would it be correct to characterize loop invariants as a type of tautology? I ask since the invariant must basically always be true, before the loop starts, before each iteration and after the loop ...
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### Counting Inversions Using Merge Sort

In Corman, Introduction To Algorithms, 3rd edition, question 2-4 it asks to count the number of inversions in a list of numbers in $\theta( n \lg n )$ time. He uses a modified Merge Sort to ...