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| | Hello. Let me introduce the writer. Her name is Refugia Shryock. One of the extremely very best issues in the globe for me is to do aerobics and now I'm trying to make cash with it. North Dakota is her birth place but she will have to transfer one day or another. I am a meter reader.<br><br>My page :: over the counter std test [[http://dtekorea.com/xe/DS_030111/1073195 see this page]] |
| {{expert-subject|1=Computer science|date=September 2011}}
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| {{technical|date=September 2011}}
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| }}
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| '''UNITY''' is a programming language that was constructed by [[K. Mani Chandy]] and [[Jayadev Misra]] for their book ''Parallel Program Design: A Foundation''. It is a rather theoretical language, which tries to focus on ''what'', instead of ''where'', ''when'' or ''how''. The peculiar thing about the language is that it has no [[flow control (data)|flow control]]. The [[statement (programming)|statement]]s in the program run in a [[random]] order, until none of the statements causes change if run. This allows for programs that run indefinitely (auto-pilot or power plant safety system) as well as programs that would normally terminate (which here converge to a [[Fixed point combinator|fixed point]]).
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| == Description ==
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| All statements are [[assignment (computer science)|assignment]]s, and are separated by <code>#</code>. A statement can consist of multiple assignments, of the form <code>a,b,c := x,y,z</code>, or <code>a := x || b := y || c := z</code>. You can also have a ''quantified statement list'', <code><# x,y : ''expression'' :: ''statement''></code>, where x and y are chosen randomly among the values that satisfy ''expression''. A ''quantified assignment'' is similar. In <code><|| x,y : ''expression'' :: ''statement'' ></code>, ''statement'' is executed simultaneously for ''all'' pairs of <code>x</code> and <code>y</code> that satisfy ''expression''.
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| ==Examples==
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| ===Bubble sort===
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| [[Bubble sort]] the array by comparing adjacent numbers, and swapping them if they are in the wrong order. Using <math>\Theta(n)</math> expected time, <math>\Theta(n)</math> processors and <math>\Theta(n^2)</math> expected work. The reason you only have <math>\Theta(n)</math> ''expected'' time, is that <code>k</code> is always chosen randomly from <math>\{0,1\}</math>. This can be fixed by flipping <code>k</code> manually.
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| Program bubblesort
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| declare
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| n: integer,
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| A: array [0..n-1] of integer
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| initially
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| n = 20 #
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| <|| i : 0 <= i and i < n :: A[i] = rand() % 100 >
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| assign
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| <# k : 0 <= k < 2 ::
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| <|| i : i % 2 = k and 0 <= i < n - 1 ::
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| A[i], A[i+1] := A[i+1], A[i]
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| if A[i] > A[i+1] > >
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| end
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| ===Rank-sort===
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| You can sort in <math>\Theta(\log n)</math> time with rank-sort. You need <math>\Theta(n^2)</math> processors, and do <math>\Theta(n^2)</math> work.
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| Program ranksort
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| declare
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| n: integer,
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| A,R: array [0..n-1] of integer
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| initially
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| n = 15 #
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| <|| i : 0 <= i < n ::
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| A[i], R[i] = rand() % 100, i >
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| assign
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| <|| i : 0 <= i < n ::
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| R[i] := <+ j : 0 <= j < n and (A[j] < A[i] or (A[j] = A[i] and j < i)) :: 1 > >
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| #
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| <|| i : 0 <= i < n ::
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| A[R[i]] := A[i] >
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| end
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| ===Floyd–Warshall algorithm===
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| Using the [[Floyd–Warshall algorithm]] all pairs [[Shortest path problem|shortest path]] algorithm, we include intermediate nodes iteratively, and get <math>\Theta(n)</math> time, using <math>\Theta(n^2)</math> processors and <math>\Theta(n^3)</math> work.
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| Program shortestpath
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| declare
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| n,k: integer,
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| D: array [0..n-1, 0..n-1] of integer
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| initially
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| n = 10 #
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| k = 0 #
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| <|| i,j : 0 <= i < n and 0 <= j < n ::
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| D[i,j] = rand() % 100 >
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| assign
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| <|| i,j : 0 <= i < n and 0 <= j < n ::
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| D[i,j] := min(D[i,j], D[i,k] + D[k,j]) > ||
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| k := k + 1 if k < n - 1
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| end
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| We can do this even faster. The following programs computes all pairs shortest path in <math>\Theta(\log^2 n)</math> time, using <math>\Theta(n^3)</math> processors and <math>\Theta(n^3 \log n)</math> work.
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| Program shortestpath2
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| declare
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| n: integer,
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| D: array [0..n-1, 0..n-1] of integer
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| initially
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| n = 10 #
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| <|| i,j : 0 <= i < n and 0 <= j < n ::
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| D[i,j] = rand() % 10 >
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| assign
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| <|| i,j : 0 <= i < n and 0 <= j < n ::
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| D[i,j] := min(D[i,j], <min k : 0 <= k < n :: D[i,k] + D[k,j] >) >
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| end
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| After round <math>r</math>, <code>D[i,j]</code> contains the length of the shortest path from <math>i</math> to <math>j</math> of length <math>0 \dots r</math>. In the next round, of length <math>0 \dots 2r</math>, and so on.
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| ==References==
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| * K. Mani Chandy and Jayadev Misra (1988) ''Parallel Program Design: A Foundation''.
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| [[Category:Experimental programming languages]]
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