From 6a05573ec8ce6538a7f3b56315ce321b815fec1c Mon Sep 17 00:00:00 2001
From: Davis King <davis@dlib.net>
Date: Sun, 21 Oct 2012 19:22:42 -0400
Subject: [PATCH] Added a BSP example.

---
 examples/CMakeLists.txt |   1 +
 examples/bsp_ex.cpp     | 157 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 158 insertions(+)
 create mode 100644 examples/bsp_ex.cpp

diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt
index 821d4e151..05c957df4 100644
--- a/examples/CMakeLists.txt
+++ b/examples/CMakeLists.txt
@@ -40,6 +40,7 @@ add_example(bayes_net_ex)
 add_example(bayes_net_from_disk_ex)
 add_example(bayes_net_gui_ex)
 add_example(bridge_ex)
+add_example(bsp_ex)
 add_example(compress_stream_ex)
 add_example(config_reader_ex)
 add_example(custom_trainer_ex)
diff --git a/examples/bsp_ex.cpp b/examples/bsp_ex.cpp
new file mode 100644
index 000000000..1c1423344
--- /dev/null
+++ b/examples/bsp_ex.cpp
@@ -0,0 +1,157 @@
+// The contents of this file are in the public domain. See LICENSE_FOR_EXAMPLE_PROGRAMS.txt
+/*
+
+    This is an example illustrating the use of the Bulk Synchronous Parallel 
+    processing tools from the dlib C++ Library.
+
+
+*/
+
+
+
+
+
+#include "dlib/cmd_line_parser.h"
+#include "dlib/bsp.h"
+#include "dlib/matrix.h"
+
+#include <iostream>
+
+typedef dlib::cmd_line_parser<char>::check_1a_c clp_parser;
+
+using namespace std;
+using namespace dlib;
+
+// ----------------------------------------------------------------------------------------
+
+double f ( double x)
+{
+    return std::pow(x-2.0, 2.0);
+}
+
+// ----------------------------------------------------------------------------------------
+
+void bsp_job_node_0 (
+    bsp_context& context,
+    double& min_value,
+    double& optimal_x
+)
+{
+    double left = -100;
+    double right = 100;
+
+    min_value = std::numeric_limits<double>::infinity();
+    double interval_width = std::abs(right-left);
+
+    for (int i = 0; i < 10000; ++i)
+    {
+        context.broadcast(left);
+        context.broadcast(right);
+
+        for (unsigned int k = 1; k < context.number_of_nodes(); ++k)
+        {
+            std::pair<double,double> val;
+            context.receive(val);
+            if (val.second < min_value)
+            {
+                min_value = val.second;
+                optimal_x = val.first;
+            }
+        }
+
+        interval_width *= 0.5;
+        left  = optimal_x - interval_width/2;
+        right = optimal_x + interval_width/2;
+    }
+}
+
+// ----------------------------------------------------------------------------------------
+
+void bsp_job_other_nodes (
+    bsp_context& context,
+    long grid_resolution
+)
+{
+    double left, right;
+    while (context.try_receive(left))
+    {
+        context.receive(right);
+
+        const double l = (context.node_id()-1)/(context.number_of_nodes()-1.0);
+        const double r = context.node_id()    /(context.number_of_nodes()-1.0);
+
+        const double width = right-left;
+        const matrix<double> values_to_check = linspace(left+l*width, left+r*width, grid_resolution);
+
+        double best_x;
+        double best_val = std::numeric_limits<double>::infinity();
+        for (long j = 0; j < values_to_check.size(); ++j)
+        {
+            double temp = f(values_to_check(j));
+            if (temp < best_val)
+            {
+                best_val = temp;
+                best_x = values_to_check(j);
+            }
+        }
+
+        context.send(make_pair(best_x, best_val), 0);
+    }
+}
+
+// ----------------------------------------------------------------------------------------
+
+int main(int argc, char** argv)
+{
+    try
+    {
+        clp_parser parser;
+        parser.add_option("h","Display this help message.");
+        parser.add_option("l","Run as a listening BSP node.",1);
+
+        parser.parse(argc, argv);
+        parser.check_option_arg_range("l", 1, 65535);
+
+        if (parser.option("h"))
+        {
+            // display all the command line options
+            cout << "Usage: bsp_ex (-l port | <list of hosts>)\n";
+            parser.print_options(cout); 
+            cout << endl;
+            return 0;
+        }
+
+
+        if (parser.option("l"))
+        {
+            const unsigned short listening_port = get_option(parser, "l", 0);
+            cout << "Listening in port " << listening_port << endl;
+            const long grid_resolution = 100;
+            bsp_listen(listening_port, bsp_job_other_nodes, grid_resolution);
+        }
+        else
+        {
+            if (parser.number_of_arguments() == 0)
+            {
+                cout << "You must give some listening BSP nodes as arguments to this program!" << endl;
+                return 0;
+            }
+
+            std::vector<network_address> hosts;
+            for (unsigned long i = 0; i < parser.number_of_arguments(); ++i)
+                hosts.push_back(parser[i]);
+
+            double min_value, optimal_x;
+            bsp_connect(hosts, bsp_job_node_0, dlib::ref(min_value), dlib::ref(optimal_x));
+
+            cout << "optimal_x: "<< optimal_x << endl;
+            cout << "min_value: "<< min_value << endl;
+        }
+
+    }
+    catch (std::exception& e)
+    {
+        cout << "error in main(): " << e.what() << endl;
+    }
+}
+