Difference between revisions of "Prefix sums"
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== Source Code == | == Source Code == | ||
| − | function void main | + | #include <maths> |
| − | + | #include <io> | |
| − | + | #include <string> | |
| − | + | ||
| − | + | var processes:=10; | |
| − | + | ||
| − | + | function void main(var argc:Int,var argv:array[String]) { | |
| − | + | var a:Int :: allocated[multiple[]]; | |
| − | + | var p; | |
| − | + | par p from 0 to processes - 1 { | |
| − | + | var mine:Int; // Force to be an integer as randomnumber function defaults to double | |
| − | + | mine:= randomnumber(0,toint(argv[1])); | |
| − | + | var i; | |
| − | + | for i from 0 to processes - 1 { | |
| − | + | var myvalue:=mine; | |
| + | if (i < p) myvalue:=0; | ||
| + | (a :: reduce[i, "sum"]):=myvalue; | ||
| + | }; | ||
| + | print(itostring(p)+" "+itostring(mine)+" = "+itostring(a)+"\n"); | ||
}; | }; | ||
| − | |||
| − | |||
}; | }; | ||
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Download the entire prefix sums source code [http://www.mesham.com/downloads/prefix.mesh here] | Download the entire prefix sums source code [http://www.mesham.com/downloads/prefix.mesh here] | ||
| + | |||
| + | [[Category:Example Codes]] | ||
Revision as of 13:28, 19 January 2013
Contents
Overview
Prefix sums is a very simple, basic parallel algorithm commonly used as the building block of many applications. Also known as a scan, each process will sumate their value with every preceding processes' value. For instance, p=0 returns its value, p=1 returns p=1 + p=0 values, p=2 returns p=2 + p=1 + p=0 values. The MPI reduce command often implements the communication via the logarithmic structure shown below.
Source Code
#include <maths>
#include <io>
#include <string>
var processes:=10;
function void main(var argc:Int,var argv:array[String]) {
var a:Int :: allocated[multiple[]];
var p;
par p from 0 to processes - 1 {
var mine:Int; // Force to be an integer as randomnumber function defaults to double
mine:= randomnumber(0,toint(argv[1]));
var i;
for i from 0 to processes - 1 {
var myvalue:=mine;
if (i < p) myvalue:=0;
(a :: reduce[i, "sum"]):=myvalue;
};
print(itostring(p)+" "+itostring(mine)+" = "+itostring(a)+"\n");
};
};
Notes
The function main has been included here so that the user can provide, via command line options, the range of the random number to find. The complexity of the prefix sums is taken away by using the reduce primitive communication type.
Download
Download the entire prefix sums source code here
