The science of compressing and communicating information. It is a branch of applied mathematics and electrical engineering. Though originally the focus was on digital communications and computing, it now finds wide use in biology, physics and other sciences.

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Information Theory - Uniquely Decipherable code problem

Hi I'm having trouble with parts bii) and c) of the following problem. For bii) I feel I might need to apply Markov's inequality but I'm really not sure. Edit: Think I've sorted out bii) it was not ...
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5 views

Finding the Optimal Function Composition to Maximize Goodness of Fit [on hold]

Assume I have one function $f(x)$, which optimally models empirical data in the range $[x_0, x_n]$ and a second function $g(t)$, which is optimal for the range $[x_{n+1}, x_{max}]$. $^1$ The function ...
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22 views

Shannon's definition of ergodicity

In A Mathematical Theory of Communication (1948) Shannon gives a definition of ergodicity for a Markov process. In order to be ergodic the directed graph of the process must have the following ...
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2answers
35 views

Expected time to pick up n things when I can drop them each round?

Why Can't I Hold All These Limes? Suppose I wanted to hold $n$ limes. Each time step, I pick up a lime. But limes are hard to hold, so I also have a probability $p$ to drop a lime on each step which ...
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1answer
25 views

Tutorials on LDPC error correction codes

Please consider this as soft question. Recently, I have been studying channel coding and in particular error correction codes. I am looking for best tutorial (easy to understand) on LDPC error ...
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2answers
41 views

Why is an entropy of $\text{log}(n)$ only compatible with the uniform distribution

I have a random variable $X$ and want to show that having an entropy $$ H(X) = - \sum_{i=1}^n p_i \text{log}(p_i) = \text{log}(n)$$ is equivalent to the distribution of $X$ being uniform. Starting ...
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45 views

Quantum Teleportation - how to prove the general case?

I've taken a course of quantum information theory and although I can compute a quantum teleportation in an explicit case where I'm given a quantum entanglement shared by Alice and Bob (normally ...
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1answer
18 views

Shannon's Noisy Coding Theorem

I'm confused by what it means when it says rate. At the bottom of page 15 and page 16 here http://www0.maths.ox.ac.uk/system/files/coursematerial/2014/3093/6/Lecture_notes.pdf it seems to be saying ...
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20 views

Interpreting the expression for the “typical” probability of a distribution (Information Theory)

When thinking about typical sets, I've been coming across the notion of the 'typical probability': (1) $p_{typical, X} = 2^{-H(X)}$ (2) $H(X) = -\Sigma p_{i}log(p_{i})$ = $-\Sigma ...
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2answers
34 views

Entropy Formula $\sum_i p_i log(\frac{1}{p_i})$

In my algorithms course I have been introduced to the concept of entropy and data compression, mainly using huffman encoding. I am trying to understand the formula for entropy $$\sum_i p_i ...
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1answer
59 views

Distance between theorems

In automated proving one can define the best proof of a theorem as the one which minimizes the length of the proof. Given a set of known statements one could define the difficulty of a theorem as the ...
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1answer
23 views

Entropy Calculation and derivation of logarithm

I have probabilities as $$p_1 = 0.4,\ p_2 = 0.3,\ p_3=0.2,\ p_4=0.1$$ hence entropy is given by: $$H(x) = -\big(0.4\cdot \log_2(0.4) + 0.3\cdot \log_2(0.3) + 0.2\cdot \log_2(0.2) + 0.1\cdot ...
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14 views

How to prove equality $K(x, K(x)) = K(x) + O(1) $?

It is needed to prove that $K(x, K(x))=K(x) + O(1)$ where $K$ means Kolmogorov complexity. I think the equality is true because when we find Kolmogorov complexity of $x$ we already knows $K(x)$ and ...
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21 views

Is there a perfect secret sharing scheme for any structure of access with three participants?

It is needed to check that: 1)for any structure of access with three participants there is always a perfect secret sharing scheme 2)for any structure of access with four participants there is always ...
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0answers
23 views

Why do we need ϵ>0 for typical set in Asymptotic Equipartition Property (AEP)?

In following text, author has used ϵ>0 for a typical set in AEP but it don't matter if we don't take it. Why is ϵ needed as I am seeing it a lot in information theory specially in AEPs. Can someone ...
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0answers
20 views

Confidence Interval of Information Entropy?

Information entropy, $IE$, is defined as: $$IE = \sum_{i} p_i log\frac{1}{p_i}$$ Where $p_i$ is the probability of event $i$ (and we are summing over all possible events). Let's say I have data ...
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1answer
24 views

Summation notation conversion to multiplication in attached equation.. How? Please explain.

Can any one please tell me how summation sign has been changed to multiplication in 2nd and 3rd equation and inequality also changed to equal sign.
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17 views

Finding optimal output alphabets

Let's say I have am given an input distribution, and I want to find the optimal output distribution. By "optimal" I mean that the mean squared error between output and input distribution is minimized, ...
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1answer
32 views

Question about conditional entropy.

Jointly distributed random variables (a) and (b) are distributed on the n-element set. Let $\varepsilon = Prob(a \ne b)$ It is needed to prove that $H(a|b) \le 1 + \varepsilon log(n-1)$. I tried ...
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12 views

Help me construct a bijection $g: \left(1..n\right)^m \to \left(1..n\right)^m$, with influence of each component of $x$ in each component of $g(x)$

Let $x \in \left(0..n-1\right)^m$. I want to construct a bijection $g$ : $\left(0..n-1\right)^m \to \left(0..n-1\right)^m$ such that if we know $m'$ components of $g(x)$ and $m-m'$ components of $x$, ...
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1answer
14 views

Mutual Information of Coupled channels

I am trying to determine the what the expression for the mutual information of following system would be; $Y_1$ = ($X_1$ + $\eta_1$) + A($X_2$ + $\eta_2$) $Y_2$ = B($X_1$ + $\eta_1$) + ($X_2$ + ...
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33 views

Is there an alternative encoding scheme to binary where similarity of pattern correlates with size of number?

If I compare binary for 7 111 and binary for 8 1000 there is no correlation between these two patterns that suggests that ...
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1answer
30 views

Proof of an inequality with entropy and mutual information.

Entropy of a random variable (a) is (h) : $H(a) = h$. Mutual information of (a) and (b) is (3h/4) : $I(a;b) = 3h/4$. Mutual information of (a) and (c) is (3h/4) : $I(a;c) = 3h/4$. It is needed to ...
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37 views

Linearity of codes

Assuming $C$ is a binary linear code and let $a$ $\notin $ $C$ be any vector. Show that $C$ $\cup (a + C) $ is also linear. I know that for any $C_1,C_2 \in C $ then $\alpha C_1 + \beta C_2 \in C$ ...
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69 views

Vector distance of binary

Suppose $\overline{u},\overline{v},\overline{w},\overline{x}$ are four binary vectors, pairwise distance d apart. Show that d must be even, there's exactly one vector which is a distance $d\over 2$ ...
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22 views

What are some techniques of specifying a molecules structure using the least amount of information?

For instance say I have a water molecule I can describe it's structure by two bond lengths and a bond angle. Are there any neat math tricks or representations of objects that I could use to describe ...
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27 views

Constructor Theory: Why does $y\subset z$ imply $y \not \bot z$?

In the paper Constructor Theory of Information, page 11. We are told that a set $X$ of attributes are distinguishable if the following is a possible task: $$\{ x\rightarrow \Psi_x | x\in X \}$$ where ...
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2answers
27 views

Mutual information expressed as Kullback-Leibler divergence

My lecturer defines the mutual information: $$ I(X;Y\mid Z) = D_{KL}\big(p(X,Y\mid Z)\parallel p(X\mid Z)\;p(Y\mid Z)\big)$$ Is this correct? I feel like it doesn't really make sense to say that; ...
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23 views

Proof that the inequality with mutual information and conditional mutual information is not true always.

It is needed to prove that inequality $I(a:b) \le I(a:b|x) + I(a:b|y) + I(x:y)$ (where I(a:b) is mutual information and I(a:b|x) is conditional mutual information) is true not for all sets of random ...
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1answer
95 views

Using Markov Chains to simplify mutual information expressions

I read a paper in Information Theory which claims that the following sum of three mutual information expressions $$ I(Y_1;X_1,X_2,X_3)+I(Y_2;X_2,X_3\mid Y_1,X_1)+I(Y_3;X_3\mid Y_1,Y_2,X_1,X_2)\tag1$$ ...
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22 views

Task about Hartley information(logarithm from cardinality of the set) of a number of paths in a graph and about limit linked with this information.

Let $L_n$ be the number of all paths of length n in a directed graph(below). It is needed to find $lim_{n \to \infty}\chi(L_n)/n$ where $\chi(L_n)$ is Hartley information in $L_n$ set. (If I am not ...
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1answer
40 views

Existing of a distribution of three random variables that have conditional mutual information with defined properties.

I have two similar questions: 1)Does exist a distribution of three random variables such that: $I(a:b) = 0$ and $I(a:b|c)>0$ (where $I(a:b)$ is a mutual information and $I(a:b|c)$ is a ...
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1answer
112 views

Guessing number in set 1-100 with weighted questions.

It is needed to guess number from 1 to 100. I can ask questions and get answers:"yes" or "no". For the "yes"-answer I must pay one dollar, for the "no"-answer - two dollars. How many dollars should I ...
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1answer
23 views

Why does the information content of a less probable event yield more bits than a more probable one?

I gather for a series of four coin flips, if we get $H,H,H,H$, this has a probability of $\tfrac{1}{16}$, so we have information content $$\log_2 \frac{1}{\frac{1}{16}}$$ But for the rest of the ...
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46 views

Proof of an inequality about set in four-dimensional space

It is needed to prove that for set $A \subset N^4$ $3\log|A|\le \log|\pi_{1,2,3}(A)|+\log|\pi_{1,2,4}(A)|+\log|\pi_{1,3,4}(A)|+\log|\pi_{2,3,4}(A)|$ where $\pi_{i,j,k}(A)$ is a projection of $A$ on ...
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1answer
48 views

The mutual information rate spectrum

Definition: $\mathbf{X}$ denotes the random vector $({X_1},{X_2},...,{X_n})$. The mutual information between $X$ and $Y$, $I(X;Y)$, is determined by the joint law of $p(X,Y)$, Given two random ...
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1answer
28 views

Decomposability of Inf. Entropy applied to corpus statistics

Can you help me understand the additivity property of IE? I think I may have found a violation but it may be that I'm just misunderstanding the maths. I'm attempting to achieve a meaningful ...
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1answer
40 views

How to understand the product of two conditional probabilities?

I am struggling a little bit with making sense of the distribution of bigrams in an artificial language I randomly generated from english. Every word occurs with an equal probability but the ...
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1answer
23 views

Confused By Information Diagram

I'm working on information theory and I get confused by the information(venn) diagram. Is there any one help me with the following confusion? As defined, mutual information $I(X;Y)$(Figure a) is ...
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1answer
20 views

Understanding Conditional Mutual Information

Recently I'm working on conditional mutual information and I'm trying to prove the following property: I(X;Y|Z,W)<=I(X;Y|Z) The property seems obvious to me: ...
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1answer
23 views

Finding error control capability of Hamming distance

I have known how to calculate the Hamming distance between two message codes. But I don't know how to get the error control capability. In one case I have hamming distance of: $$ d = 8 $$ Errors ...
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1answer
20 views

Mutual Information Gaussian

Suppose $x$ has a multivariate Gaussian distribution given by $\mathcal{N}(\mu , \Sigma)$. How do you express the mutual information between two coordinates that is $\mathrm{I}(x_i;x_j)$ , as a ...
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17 views

Proof of inequality about mutual information

There is some joint distribution of random variables $(a, b, c, x, y)$. It is known that $I(a;b|c) = I(a;c|b) = I(b;c|a) = 0$ It is needed to prove this inequality: $I(a;b) \leq I(a;b|x) + I(a;b|y) + ...
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21 views

Kolmogorov complexity inequality

Prove, that KP (x) ≤ KS (x) + log KS(x) + 2 log log KS (x) + O(1). Please tell me in which direction to think.
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15 views

Optimal Kolmogorov complexity

Let computable function U is the best way to describe to Kolmogorov complexity. Prove that the mapping V, determined crucial for any word p as V (p) = U (U (p)), is also optimal way to describe the. ...
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29 views

Proof of a fact about mutual information and entropy

It is needed to prove that for distribution (a, b, c) such that $I(a;b|c) = I(a;c|b) = I(b;c|a) = 0$ exists a random variable $d$ such that $H(d) = I(a, b, c)$ and $a,b,c$ are independent with ...
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1answer
38 views

Proof of inequality with entropy

I can not prove this inequality $2H(a,b,c) \leq H(a,b) + H(a,c) + H(b,c|a),\ H-entropy $. I tried do it by using chain rule and this inequality $H(X|Y) \leq H(X;Y)$ but without any success. Please ...
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1answer
24 views

Questions Regarding Mutual Information

I've been conducting a small experiment to test a few of my interpretations about mutual information, and I'm running into some difficulties. I've created some MATLAB code that basically makes two ...
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30 views

Capacity of uniform noise channel

I'm pretty sure I've made some error in reasoning in this exercise because it gets a little bit too easy. Let $X$ be independent from $N$ where $N$ is uniformly distributed over $[-1,1]$. Suppose ...
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1answer
31 views

a question about entropy of run length coding

I'm doing an exercise from chapter two of $\textit {elements of information theory}$. Here is the problem and its solution, . I'm not very clear about the equation 2.36 or say why does the equation ...