UNITY (programming language)
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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 theoretical language, which tries to focus on what, instead of where, when or how. The language has no flow control, the statements in the program run in an nondeterministic way, until none of the statements causes change if executed. 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).
All statements are assignments, and are separated by
#. A statement can consist of multiple assignments, of the form
a,b,c := x,y,z, or
a := x || b := y || c := z. You can also have a quantified statement list,
<# x,y : expression :: statement>, where x and y are chosen randomly among the values that satisfy expression. A quantified assignment is similar. In
<|| x,y : expression :: statement >, statement is executed simultaneously for all pairs of
y that satisfy expression.
Bubble sort the array by comparing adjacent numbers, and swapping them if they are in the wrong order. Using expected time, processors and expected work. The reason you only have expected time, is that
k is always chosen randomly from . This can be fixed by flipping
Program bubblesort declare n: integer, A: array [0..n-1] of integer initially n = 20 # <|| i : 0 <= i and i < n :: A[i] = rand() % 100 > assign <# k : 0 <= k < 2 :: <|| i : i % 2 = k and 0 <= i < n - 1 :: A[i], A[i+1] := A[i+1], A[i] if A[i] > A[i+1] > > end
You can sort in time with rank-sort. You need processors, and do work.
Program ranksort declare n: integer, A,R: array [0..n-1] of integer initially n = 15 # <|| i : 0 <= i < n :: A[i], R[i] = rand() % 100, i > assign <|| i : 0 <= i < n :: R[i] := <+ j : 0 <= j < n and (A[j] < A[i] or (A[j] = A[i] and j < i)) :: 1 > > # <|| i : 0 <= i < n :: A[R[i]] := A[i] > end
Program shortestpath declare n,k: integer, D: array [0..n-1, 0..n-1] of integer initially n = 10 # k = 0 # <|| i,j : 0 <= i < n and 0 <= j < n :: D[i,j] = rand() % 100 > assign <|| i,j : 0 <= i < n and 0 <= j < n :: D[i,j] := min(D[i,j], D[i,k] + D[k,j]) > || k := k + 1 if k < n - 1 end
We can do this even faster. The following programs computes all pairs shortest path in time, using processors and work.
Program shortestpath2 declare n: integer, D: array [0..n-1, 0..n-1] of integer initially n = 10 # <|| i,j : 0 <= i < n and 0 <= j < n :: D[i,j] = rand() % 10 > assign <|| i,j : 0 <= i < n and 0 <= j < n :: D[i,j] := min(D[i,j], <min k : 0 <= k < n :: D[i,k] + D[k,j] >) > end
After round ,
D[i,j] contains the length of the shortest path from to of length . In the next round, of length , and so on.
- K. Mani Chandy and Jayadev Misra (1988) Parallel Program Design: A Foundation.