scholarly journals Lower-Bound Synthesis Using Loop Specialization and Max-SMT

2021 ◽  
pp. 863-886
Author(s):  
Elvira Albert ◽  
Samir Genaim ◽  
Enrique Martin-Martin ◽  
Alicia Merayo ◽  
Albert Rubio
Keyword(s):  
Lower Bound ◽  
Lower Bounds ◽  
Soft Constraints ◽  
Worst Case ◽  
New Framework

AbstractThis paper presents a new framework to synthesize lower-bounds on the worst-case cost for non-deterministic integer loops. As in previous approaches, the analysis searches for a metering function that under-approximates the number of loop iterations. The key novelty of our framework is the specialization of loops, which is achieved by restricting their enabled transitions to a subset of the inputs combined with the narrowing of their transition scopes. Specialization allows us to find metering functions for complex loops that could not be handled before or be more precise than previous approaches. Technically, it is performed (1) by using quasi-invariants while searching for the metering function, (2) by strengthening the loop guards, and (3) by narrowing the space of non-deterministic choices. We also propose a Max-SMT encoding that takes advantage of the use of soft constraints to force the solver look for more accurate solutions. We show our accuracy gains on benchmarks extracted from the 2020 Termination and Complexity Competition by comparing our results to those obtained by the "Image missing" system.

scholarly journals Lower Bounds for Dynamic Transitive Closure, Planar Point Location, and Parentheses Matching

1996 ◽  
Vol 3 (9) ◽  
Author(s):  
Thore Husfeldt ◽  
Theis Rauhe ◽  
Søren Skyum
Keyword(s):  
Lower Bound ◽  
Lower Bounds ◽  
Transitive Closure ◽  
Unit Cost ◽  
Random Access ◽  
Point Location ◽  
Worst Case ◽  
Planar Point ◽  
Planar Point Location ◽  
Prefix Sums

We give a number of new lower bounds in the cell probe model<br />with logarithmic cell size, which entails the same bounds on the random access computer with logarithmic word size and unit cost operations. We study the signed prefix sum problem: given a string of length n of zeroes and signed ones, compute the sum of its ith prefix during updates. We show a<br />lower bound of  Omega(log n/log log n) time per operations, even if the prefix sums are bounded by log n/log log n during all updates. We also show that if the update time is bounded by the product of the worst-case update time and the<br />answer to the query, then the update time must be Omega(sqrt(log n/ log log n)).<br /> These results allow us to prove lower bounds for a variety of seemingly unrelated<br />dynamic problems. We give a lower bound for the dynamic planar point location in monotone subdivisions of <br />Omega(log n/ log log n) per operation. We give<br />a lower bound for the dynamic transitive closure problem on upward planar graphs with one source and one sink of <br />Omega(log n/(log logn)^2) per operation. We give a lower bound of  Omega(sqrt(log n/log log n)) for the dynamic membership problem of any Dyck language with two or more letters. This implies the same<br />lower bound for the dynamic word problem for the free group with k generators. We also give lower bounds for the dynamic prefix majority and prefix equality problems.

scholarly journals Lower Bounds for Dynamic Algebraic Problems

1998 ◽  
Vol 5 (11) ◽  
Author(s):  
Gudmund Skovbjerg Frandsen ◽  
Johan P. Hansen ◽  
Peter Bro Miltersen
Keyword(s):  
Fourier Transform ◽  
Lower Bound ◽  
Lower Bounds ◽  
Communication Complexity ◽  
Symmetric Functions ◽  
Matrix Multiplication ◽  
Worst Case ◽  
Dynamic Matrix ◽  
Wide Range ◽  
On Line

We consider dynamic evaluation of algebraic functions (matrix multiplication, determinant, convolution, Fourier transform, etc.) in the model of Reif and Tate; i.e., if f(x1, . . . , xn) = (y1, . . . , ym) is an algebraic problem, we consider serving on-line requests of the form "change input xi to value v" or "what is the value of output yi?". We present techniques for showing lower bounds on the worst case time complexity per operation for such problems. The first gives lower bounds in a wide range of rather powerful models (for instance history dependent<br />algebraic computation trees over any infinite subset of a field, the integer RAM, and the generalized real RAM model of Ben-Amram and Galil). Using this technique, we show optimal  Omega(n) bounds for dynamic matrix-vector product, dynamic matrix multiplication and dynamic discriminant and an <br />Omega(sqrt(n)) lower bound for dynamic polynomial multiplication (convolution), providing a good match with Reif and<br />Tate's O(sqrt(n log n)) upper bound. We also show linear lower bounds for dynamic determinant, matrix adjoint and matrix inverse and an Omega(sqrt(n)) lower bound for the elementary symmetric functions. The second technique is the communication complexity technique of Miltersen, Nisan, Safra, and Wigderson which we apply to the setting<br />of dynamic algebraic problems, obtaining similar lower bounds in the word RAM model. The third technique gives lower bounds in the weaker straight line program model. Using this technique, we show an ((log n)2= log log n) lower bound for dynamic discrete Fourier transform. Technical ingredients of our techniques are the incompressibility technique of Ben-Amram and Galil and the lower bound for depth-two superconcentrators of Radhakrishnan and Ta-Shma. The incompressibility technique is extended to arithmetic computation in arbitrary fields.

scholarly journals Lower Bounds on the Dilation of Plane Spanners

2016 ◽  
Vol 26 (02) ◽  
pp. 89-110 ◽  
Author(s):  
Adrian Dumitrescu ◽  
Anirban Ghosh
Keyword(s):  
Lower Bound ◽  
Lower Bounds ◽  
Worst Case ◽  
Stretch Factor ◽  
Geometric Spanners ◽  
Point Set ◽  
Greedy Triangulation ◽  
Text Element

(I) We exhibit a set of 23 points in the plane that has dilation at least [Formula: see text], improving the previous best lower bound of [Formula: see text] for the worst-case dilation of plane spanners. (II) For every [Formula: see text], there exists an [Formula: see text]-element point set [Formula: see text] such that the degree [Formula: see text] dilation of [Formula: see text] equals [Formula: see text] in the domain of plane geometric spanners. In the same domain, we show that for every [Formula: see text], there exists a an [Formula: see text]-element point set [Formula: see text] such that the degree [Formula: see text] dilation of [Formula: see text] equals [Formula: see text] The previous best lower bound of [Formula: see text] holds for any degree. (III) For every [Formula: see text], there exists an [Formula: see text]-element point set [Formula: see text] such that the stretch factor of the greedy triangulation of [Formula: see text] is at least [Formula: see text].

scholarly journals Fully-Dynamic and Kinetic Conflict-Free Coloring of Intervals with Respect to Points

2019 ◽  
Vol 29 (01) ◽  
pp. 49-72
Author(s):  
Mark de Berg ◽  
Tim Leijsen ◽  
Aleksandar Markovic ◽  
André van Renssen ◽  
Marcel Roeloffzen ◽  
...  
Keyword(s):  
Lower Bound ◽  
Lower Bounds ◽  
Upper And Lower Bounds ◽  
Worst Case ◽  
Insertions And Deletions ◽  
Coloring Problem ◽  
Trade Offs ◽  
Special Cases ◽  
The Cost ◽  
Case Number

We introduce the fully-dynamic conflict-free coloring problem for a set [Formula: see text] of intervals in [Formula: see text] with respect to points, where the goal is to maintain a conflict-free coloring for [Formula: see text] under insertions and deletions. A coloring is conflict-free if for each point [Formula: see text] contained in some interval, [Formula: see text] is contained in an interval whose color is not shared with any other interval containing [Formula: see text]. We investigate trade-offs between the number of colors used and the number of intervals that are recolored upon insertion or deletion of an interval. Our results include: a lower bound on the number of recolorings as a function of the number of colors, which implies that with [Formula: see text] recolorings per update the worst-case number of colors is [Formula: see text], and that any strategy using [Formula: see text] colors needs [Formula: see text] recolorings; a coloring strategy that uses [Formula: see text] colors at the cost of [Formula: see text] recolorings, and another strategy that uses [Formula: see text] colors at the cost of [Formula: see text] recolorings; stronger upper and lower bounds for special cases. We also consider the kinetic setting where the intervals move continuously (but there are no insertions or deletions); here we show how to maintain a coloring with only four colors at the cost of three recolorings per event and show this is tight.

Linear-Time Approximation Algorithms for the Max Cut Problem

1993 ◽  
Vol 2 (2) ◽  
pp. 201-210 ◽  
Author(s):  
Nguyen van Ngoc ◽  
Zsolt Tuza
Keyword(s):  
Lower Bound ◽  
Approximation Algorithms ◽  
Lower Bounds ◽  
Connected Graph ◽  
Linear Time ◽  
Worst Case ◽  
Time Approximation ◽  
Bipartite Subgraph ◽  
Max Cut Problem ◽  
Multiple Edges

Let G be a connected graph with n vertices and m edges (multiple edges allowed), and let k ≥ 2 be an integer. There is an algorithm with (optimal) running time of O(m) that finds(i) a bipartite subgraph of G with ≥ m/2 + (n − 1)/4 edges,(ii) a bipartite subgraph of G with ≥ m/2 + 3(n−1)/8 edges if G is triangle-free,(iii) a k-colourable subgraph of G with ≥ m − m/k + (n−1)/k + (k − 3)/2 edges if k ≥ 3 and G is not k-colorable.Infinite families of graphs show that each of those lower bounds on the worst-case performance are best possible (for every algorithm). Moreover, even if short cycles are excluded, the general lower bound of m − m/k cannot be replaced by m − m/k + εm for any fixed ε > 0; and it is NP-complete to decide whether a graph with m edges contains a k-colorable subgraph with more than m − m/k + εm edges, for any k ≥ 2 and ε> 0, ε < 1/k.

scholarly journals Scatter Search on a Disk

2021 ◽  
Author(s):  
Nisha Chopra
Keyword(s):  
Lower Bound ◽  
Wireless Communication ◽  
Unit Disk ◽  
Lower Bounds ◽  
Upper Bound ◽  
Scatter Search ◽  
Search Time ◽  
Communication Model ◽  
Worst Case ◽  
First Case

Consider a unit disk with two objects at unidentified locations. We examine the problem of two or more robots in search of both objects in the wireless communication model. We begin with two robots and both are needed to carry an object. Subsequently, we design several algorithms that describe robots trajectories in search of the objects. We were able to achieve a minimum worst-case search time of 6.7518 and a lower bound of 3 + π 2 . Additionally, we define two general cases and bound the worst-case search time for both. The first of the cases is for n ≥ 3 robots and an object can be moved by one robot. The second case is where we have n ≥ 3 robots and two robots are needed to carry an object. We achieve an upper bound of 1 + 2π n + sin (⌊n 2 ⌋ π n ) for the first case and an upper bound of 3 + 2π n + sin π n for the second case, with lower bounds of 2 + π n and 3 + π n respectively.

scholarly journals Scatter Search on a Disk

2021 ◽  
Author(s):  
Nisha Chopra
Keyword(s):  
Lower Bound ◽  
Wireless Communication ◽  
Unit Disk ◽  
Lower Bounds ◽  
Upper Bound ◽  
Scatter Search ◽  
Search Time ◽  
Communication Model ◽  
Worst Case ◽  
First Case

Consider a unit disk with two objects at unidentified locations. We examine the problem of two or more robots in search of both objects in the wireless communication model. We begin with two robots and both are needed to carry an object. Subsequently, we design several algorithms that describe robots trajectories in search of the objects. We were able to achieve a minimum worst-case search time of 6.7518 and a lower bound of 3 + π 2 . Additionally, we define two general cases and bound the worst-case search time for both. The first of the cases is for n ≥ 3 robots and an object can be moved by one robot. The second case is where we have n ≥ 3 robots and two robots are needed to carry an object. We achieve an upper bound of 1 + 2π n + sin (⌊n 2 ⌋ π n ) for the first case and an upper bound of 3 + 2π n + sin π n for the second case, with lower bounds of 2 + π n and 3 + π n respectively.

scholarly journals Improved Average-Case Lower Bounds for De Morgan Formula Size: Matching Worst-Case Lower Bound

2017 ◽  
Vol 46 (1) ◽  
pp. 37-57 ◽  
Author(s):  
Ilan Komargodski ◽  
Ran Raz ◽  
Avishay Tal
Keyword(s):  
Lower Bound ◽  
Lower Bounds ◽  
Worst Case ◽  
Average Case

A Lower Bound for Schur Numbers and Multicolor Ramsey Numbers

10.37236/1188 ◽  
1994 ◽  
Vol 1 (1) ◽  
Author(s):  
Geoffrey Exoo
Keyword(s):  
Lower Bound ◽  
Lower Bounds ◽  
Ramsey Numbers

For $k \geq 5$, we establish new lower bounds on the Schur numbers $S(k)$ and on the k-color Ramsey numbers of $K_3$.

scholarly journals A Lower Bound for the Query Phase of Contraction Hierarchies and Hub Labels and a Provably Optimal Instance-Based Schema

Algorithms ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 164
Author(s):  
Tobias Rupp ◽  
Stefan Funke
Keyword(s):  
Lower Bound ◽  
Lower Bounds ◽  
Real World ◽  
Road Network ◽  
Upper And Lower Bounds ◽  
Bounded Degree ◽  
Shortest Path Routing ◽  
Graph Classes ◽  
Speed Up ◽  
To Come

We prove a Ω(n) lower bound on the query time for contraction hierarchies (CH) as well as hub labels, two popular speed-up techniques for shortest path routing. Our construction is based on a graph family not too far from subgraphs that occur in real-world road networks, in particular, it is planar and has a bounded degree. Additionally, we borrow ideas from our lower bound proof to come up with instance-based lower bounds for concrete road network instances of moderate size, reaching up to 96% of an upper bound given by a constructed CH. For a variant of our instance-based schema applied to some special graph classes, we can even show matching upper and lower bounds.

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