UNITY is a programming language constructed by
K. Mani Chandy and
Jayadev Misra
Jayadev Misra is an Indian-born computer scientist who has spent most of his professional career in the United States. He is the Schlumberger Centennial Chair Emeritus in computer science and a University Distinguished Teaching Professor Emeritus ...
for their book ''Parallel Program Design: A Foundation''. It is a theoretical language which focuses on ''what'', instead of ''where'', ''when'' or ''how''. The language contains no method of
flow control, and program
statements run in a
nondeterministic way until statements cease to cause changes during execution. This allows for programs to run indefinitely, such as auto-pilot or power plant safety systems, as well as programs that would normally terminate (which here converge to a
fixed point).
Description
All statements are
assignment
Assignment, assign or The Assignment may refer to:
* Homework
* Sex assignment
* The process of sending National Basketball Association players to its development league; see
Computing
* Assignment (computer science), a type of modification to ...
s, 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
x
and
y
that satisfy ''expression''.
Examples
Bubble sort
Bubble sort
Bubble sort, sometimes referred to as sinking sort, is a simple sorting algorithm that repeatedly steps through the input list element by element, comparing the current element with the one after it, swapping their values if needed. These passes ...
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
k
manually.
Program bubblesort
declare
n: integer,
A: array
..n-1of integer
initially
n = 20 #
<, , i : 0 <= i and i < n :: A
= rand() % 100 >
assign
<# k : 0 <= k < 2 ::
<, , i : i % 2 = k and 0 <= i < n - 1 ::
A
A
+1:= A
+1 A
if A
> A
+1> >
end
Rank-sort
You can sort in
time with rank-sort. You need
processors, and do
work.
Program ranksort
declare
n: integer,
A,R: array
..n-1of integer
initially
n = 15 #
<, , i : 0 <= i < n ::
A
R
= rand() % 100, i >
assign
<, , i : 0 <= i < n ::
R
:= <+ j : 0 <= j < n and (A
< A
or (A
= A
and j < i)) :: 1 > >
#
<, , i : 0 <= i < n ::
A
[i_:=_A_
>
_end
_Floyd–Warshall_algorithm
Using_the_[i_:=_A_
>
_end
_Floyd–Warshall_algorithm
Using_the_Floyd–Warshall_algorithm">.html"_;"title="[i">[i_:=_A_>
_end
_Floyd–Warshall_algorithm
Using_the_Floyd–Warshall_algorithm_all_pairs_Shortest_path_problem.html" "title="Floyd–Warshall_algorithm.html" ;"title=".html" ;"title="[i">[i := A >
end
Floyd–Warshall algorithm
Using the Floyd–Warshall algorithm">.html" ;"title="[i">[i := A >
end
Floyd–Warshall algorithm
Using the Floyd–Warshall algorithm all pairs Shortest path problem">shortest path
In graph theory, the shortest path problem is the problem of finding a path between two vertices (or nodes) in a graph such that the sum of the weights of its constituent edges is minimized.
The problem of finding the shortest path between tw ...
algorithm, we include intermediate nodes iteratively, and get time, using processors and work.
Program shortestpath
declare
n,k: integer,
D: array ..n-1, 0..n-1of integer
initially
n = 10 #
k = 0 #
<, , i,j : 0 <= i < n and 0 <= j < n ::
D ,j= rand() % 100 >
assign
<, , i,j : 0 <= i < n and 0 <= j < n ::
D ,j:= min(D ,j D ,k+ D ,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 ..n-1, 0..n-1of integer
initially
n = 10 #
<, , i,j : 0 <= i < n and 0 <= j < n ::
D ,j= rand() % 10 >
assign
<, , i,j : 0 <= i < n and 0 <= j < n ::
D ,j:= min(D ,j ,k+ D ,j>) >
end
After round , D ,j/code> contains the length of the shortest path from to of length . In the next round, of length , and so on.
References
* K. Mani Chandy and Jayadev Misra (1988) ''Parallel Program Design: A Foundation''.
Experimental programming languages