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luku24.tex
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luku24.tex
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@ -85,7 +85,7 @@ corresponds to the set
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Each outcome $x$ is assigned a probability $p(x)$.
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Each outcome $x$ is assigned a probability $p(x)$.
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Furthermore, the probability $P(A)$ of an event
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Furthermore, the probability $P(A)$ of an event
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that corresponds to a set $A$ can be calcuted as a sum
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that corresponds to a set $A$ can be calculated as a sum
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of probabilities of outcomes using the formula
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of probabilities of outcomes using the formula
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\[P(A) = \sum_{x \in A} p(x).\]
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\[P(A) = \sum_{x \in A} p(x).\]
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For example, when throwing a dice,
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For example, when throwing a dice,
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@ -135,7 +135,7 @@ Here $5/6$ is the probability that the outcome
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of a single throw is not six, and
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of a single throw is not six, and
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$(5/6)^{10}$ is the probability that none of
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$(5/6)^{10}$ is the probability that none of
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the ten throws is a six.
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the ten throws is a six.
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The complement of this is the answer for the problem.
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The complement of this is the answer to the problem.
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\subsubsection{Union}
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\subsubsection{Union}
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@ -164,7 +164,7 @@ the probability of the event $A \cup B$ is simply
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The \key{conditional probability}
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The \key{conditional probability}
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\[P(A | B) = \frac{P(A \cap B)}{P(B)}\]
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\[P(A | B) = \frac{P(A \cap B)}{P(B)}\]
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is the probability $A$
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is the probability of $A$
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assuming that $B$ happens.
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assuming that $B$ happens.
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In this situation, when calculating the
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In this situation, when calculating the
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probability of $A$, we only consider the outcomes
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probability of $A$, we only consider the outcomes
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@ -172,7 +172,7 @@ that also belong to $B$.
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Using the above sets,
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Using the above sets,
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\[P(A | B)= 1/3,\]
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\[P(A | B)= 1/3,\]
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Because the outcomes of $B$ are
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because the outcomes of $B$ are
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$\{1,2,3\}$, and one of them is even.
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$\{1,2,3\}$, and one of them is even.
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This is the probability of an even result
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This is the probability of an even result
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if we know that the result is between $1 \ldots 3$.
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if we know that the result is between $1 \ldots 3$.
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@ -318,7 +318,7 @@ The expected value for $X$ in a uniform distribution is
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\index{binomial distribution}
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\index{binomial distribution}
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~\\
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~\\
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In a \key{binomial distribution}, $n$ attempts
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In a \key{binomial distribution}, $n$ attempts
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are done
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are made
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and the probability that a single attempt succeeds
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and the probability that a single attempt succeeds
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is $p$.
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is $p$.
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The random variable $X$ counts the number of
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The random variable $X$ counts the number of
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@ -413,7 +413,7 @@ The next distribution is $[0,1,0,0,0]$,
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because we can only move from floor 1 to floor 2.
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because we can only move from floor 1 to floor 2.
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After this, we can either move one floor up
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After this, we can either move one floor up
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or one floor down, so the next distribution is
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or one floor down, so the next distribution is
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$[1/2,0,1/2,0,0]$, etc.
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$[1/2,0,1/2,0,0]$, and so on.
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An efficient way to simulate the walk in
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An efficient way to simulate the walk in
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a Markov chain is to use dynamic programming.
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a Markov chain is to use dynamic programming.
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@ -510,7 +510,7 @@ the array in increasing order.
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It is easy to calculate any order statistic
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It is easy to calculate any order statistic
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in $O(n \log n)$ time by sorting the array,
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in $O(n \log n)$ time by sorting the array,
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but is it really needed to sort the entire array
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but is it really needed to sort the entire array
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to just find one element?
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just to find one element?
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It turns out that we can find order statistics
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It turns out that we can find order statistics
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using a randomized algorithm without sorting the array.
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using a randomized algorithm without sorting the array.
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@ -675,7 +675,7 @@ both colors is $1/2$.
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In a random coloring, the probability that the endpoints
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In a random coloring, the probability that the endpoints
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of a single edge have different colors is $1/2$.
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of a single edge have different colors is $1/2$.
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Hence, the expected number of edges whose endpoints
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Hence, the expected number of edges whose endpoints
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have different colors is $1/2 \cdot m = m/2$.
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have different colors is $m/2$.
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Since it is excepted that a random coloring is valid,
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Since it is excepted that a random coloring is valid,
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we will quickly find a valid coloring in practice.
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we will quickly find a valid coloring in practice.
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