# Questions tagged [online-algorithms]

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### Online assignment lower bound results

I am reading the following paper which presents a $(1-\epsilon)$-competitive online algorithm for the MaxMin (similar to the makespan) problem, defined as follows: a set of requests are arriving in an ...
100 views

### On-line pagerank in a streaming DAG (Directed Acyclic Graph)

Assume a DAG (Directed Acyclic Graph) is given as a stream of edges such that edge $(u,v)$ is given only after all incoming edges of $u$ are given. Let us denote by $n$ and $m$ the number of vertices ...
1 vote
46 views

### Dynamic permutation cycle data

Let $\pi \in S_n$ be a permutation of $\{1, \ldots, n\}$. Does there exist a simple data structure that admits the following operations in polylogarithmic time? sameCycle($\pi,x,y$): determines ...
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### Is there a competitive algorithm for this online scheduling problem to minimize the truncated gaps?

Time is discrete. There are $n$ time-slots and a single job that can be scheduled on one machine of budget $B$. If the job is scheduled at time-slot $t$, then it will consume $c(t)$ units of the ...
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### Incremental PDA emptiness testing?

Is there anything known about the problem of incremental emptiness testing for a pushdown automata? Suppose you have a PDA with (up to) $n$ states and transitions, but instead of being given the ...
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### Using martingale arguments to prove convergence of iterative algorithms

Can someone give me typical/educative examples of how martingales can be used to prove convergence of an iterative algorithmS? The examples I know of can only go so far as to show that there exists ...
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1 vote
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### What is the state of the art in first order stochastic convex optimization?

What is the optimally fastest convex risk minimizing algorithm which only uses a stochastic first order oracle? Is this SGD? What is the optimally fastest convex function minimizing algorithm which ...
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218 views

### A Simple Auction Game

You are playing the following game. You have a budget of $B$ dollars. There are $n$ days. Every day $d$, you have to make a bid $b_d\geq0$ that does not exceed your budget. After making the bid, a ...
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1 vote
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### How to design an online algorithm for secretary problem with multiple players?

We have $k$ bins of capacity $c_i$ each. These bins appear in an online fashion, say on day $i$, bin $i$ appears. There are $l$ balls. Ball $j$ has weight $w_{ij}$ with bin $i$. Each ball knows that ...
• 325
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### Solving an online problem without maximizing or minimizing an objective

You have a budget $B$ and a satisfaction level $L$. An indivisible product is available for sell and you are interested in buying. The product is divided into $n$ parts. Part $i$ of the product has ...
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### What is the competitive ratio of a $d$-way associative LRU cache?

In a caching problem, items arrive online, and the algorithm needs to decide which elements to keep in the cache. If the current item is not cached, we pay a penalty of $1$. It is well known that for ...
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1 vote
240 views

### Does every online algorithm has an offline counterpart?

According to the wikipedia page for Online algorithms, it states: "Not every online algorithm has an offline counterpart." At the time of asking this question there is no citation for this claim. ...
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### Is there any online problem that the best known competitive ratio is better than the hardness of approximation (or the best known approximation)?

In online-setting, we usually allow exponential time to think and come up with a strategy. On the other hand, in offline-setting, we might care about solving a particular problem optimally, or as good ...
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1 vote
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### Searching for the original definition of online algorithms

I'm currently searching for the original formal definition of online algorithms. The earliest mentions of online algorithms that I found are from the mid 80s. But none of these papers seem to be the ...
66 views

### Efficient Online Algorithms for Matrix rank

Suppose, we have a matrix with known rank. Then, in each step one element of this matrix will be changed. Is there any efficient online algorithm to find rank of each matrix after each element update?
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1 vote
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### Problem dependent lower bound for stochastic bandits with full information

Suppose you have a $K$ armed stochastic bandit problem but with full information. There are $K$ arms with mean rewards $\mu_1,...,\mu_K$. At each step we have to select an arm, collect the reward from ...
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### Algorithms in preprocessed universe [closed]

In celebrated paper Clustered integer 3SUM via additive combinatorics by TM Chan and M Lewenstein one of the provided algorithms is the one for preprocessed universe. They were able to provide an ...
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### Online triangle counting

Please consider the following problem. It can (but probably shouldn't) be called offline version of online triangle detection on subgraphs. Given a graph $G$ and a collection $C$ of subsets of ...
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### Competitive ratio of Move To Front in alternate access - List Update Problem

I need to prove that the modification of MTF, Move to front on every even request of an element, list update problem has a competitive ratio of 2. How does one go about proving such results? (I'm ...
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### Can a non-competitive deterministic algorithm be k-competitive if randomized?

Let's say there is a problem in which all possible deterministic online algorithms tha solve this problem are not-competitive. Does this mean that a randomized online algorithm for the same problem ...
356 views

### View of Multiplicative Weights in contexts of combinatorial optimization, low-regret/online optimization, and entropy-regularized gradient descent?

Also called exponentiated gradient. I understand these are three places where multiplicative weights shows up (i.e. $w_{t+1} = w_{t}e^{- \text{loss}(w_{t})}$ or variations. And I understand a bit ...
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### Brackets expression incremental parsing algorithm

I am looking for efficient and easy in implementation algorithm for incremental parsing of expressions with brackets. Consider the example with expression like "((1)())(2)". Parse tree for that ...
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### maintaining a balanced spanning tree of a growing undirected graph

I am looking for ways to maintain a relatively balanced spanning tree of a graph, as I add new nodes/edges to the graph. I have an undirected graph that starts as a single node, the "root". At each ...
2k views

### What's the difference between online and incremental optimization?

Recently I've read some stuff about incremental optimization problems, but I can't see what's the difference between those and online optimization problems. My impression is that I can define every ...
522 views

### Is there a constant factor approximation algorithm for 2D rectangle coloring problem?

The problem we consider here is the extension of the well-known interval coloring problem. Instead of intervals we consider rectangles having sides parallel to axes. The objective is to color the ...
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### Is there an online-algorithm to keep track of components in a changing undirected graph?

Problem I have an undirected graph (with multi-edges), which will change over time, nodes and edges may be inserted and deleted. On each modification of the graph, I have to update the connected ...
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### Algorithm for 'k'' most frequently occurring numbers

I have been searching for the most efficient (streaming??) algorithm that tells me the 'k' most frequently occurring elements in a data stream at any point in time. This post: "Divide and conquer&...
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