XM_40017/notebooks/tsp.ipynb

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "8850d90e",
   "metadata": {},
   "outputs": [],
   "source": [
    "using Distributed"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "5d4935ee",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "4-element Vector{Int64}:\n",
       " 2\n",
       " 3\n",
       " 4\n",
       " 5"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "if procs() == workers()\n",
    "    addprocs(4)\n",
    "end"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "4a2756ae",
   "metadata": {},
   "outputs": [],
   "source": [
    "@everywhere function visited(city,hops,path)\n",
    "    for i = 1:hops\n",
    "        if path[i] == city\n",
    "            return true\n",
    "        end\n",
    "    end\n",
    "    return false\n",
    "end"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "id": "39e9e667",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "tsp_serial_impl (generic function with 1 method)"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "function tsp_serial_impl(connections,hops,path,current_distance,min_distance)\n",
    "    num_cities = length(connections)\n",
    "    if hops == num_cities\n",
    "        if current_distance < min_distance\n",
    "            return current_distance\n",
    "        end\n",
    "    else\n",
    "        current_city = path[hops]\n",
    "        next_hops = hops + 1\n",
    "        for (next_city,distance_increment) in connections[current_city]\n",
    "            if !visited(next_city,hops,path)\n",
    "                path[next_hops] = next_city\n",
    "                next_distance = current_distance + distance_increment\n",
    "                if next_distance < min_distance\n",
    "                    return tsp_serial_impl(connections,next_hops,path,next_distance,min_distance)\n",
    "                end\n",
    "            end\n",
    "        end        \n",
    "    end\n",
    "    min_distance\n",
    "end"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "id": "83b58881",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "tsp_serial (generic function with 1 method)"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "function tsp_serial(connections,city)\n",
    "    num_cities = length(connections)\n",
    "    path=zeros(Int,num_cities)\n",
    "    hops = 1\n",
    "    path[hops] = city\n",
    "    current_distance = 0\n",
    "    min_distance = typemax(Int)\n",
    "    min_distance = tsp_serial_impl(connections,hops,path,current_distance,min_distance)\n",
    "    (;path=path,distance=min_distance)\n",
    "end"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "id": "78095098",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "(path = [1, 4, 5, 2, 3, 6], distance = 222)"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "connections = [\n",
    "    [(1,0),(4,39),(5,76), (6,78),(3,94),(2,97)],\n",
    "    [(2,0),(5,25),(4,58),(3,62),(1,97),(6,109)],\n",
    "    [(3,0),(6,58),(2,62),(4,68),(5,70),(1,94)],\n",
    "    [(4,0),(5,38),(1,39),(2,58),(3,68),(6,78)],\n",
    "    [(5,0),(2,25),(4,38),(3,70),(1,76),(6,104)],\n",
    "    [(6,0),(3,58),(1,78),(4,78),(5,104),(2,109)]\n",
    "]\n",
    "city = 1\n",
    "tsp_serial(connections,city)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "id": "03f0dd8e",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "(path = [1, 4, 5, 2, 3, 6], distance = 222)"
      ]
     },
     "execution_count": 10,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "@everywhere function tsp_dist_impl(connections,hops,path,current_distance,min_distance,max_hops,jobs_chnl,ftr_result)\n",
    "    num_cities = length(connections)\n",
    "    if hops == num_cities\n",
    "        if current_distance < min_distance\n",
    "            if ftr_result !== nothing\n",
    "                @spawnat 1 begin\n",
    "                    result = fetch(ftr_result)\n",
    "                    result.path .= path\n",
    "                    result.min_distance_ref[] = current_distance\n",
    "                end |> wait\n",
    "            end\n",
    "            return current_distance\n",
    "        end\n",
    "    elseif hops <= max_hops\n",
    "        current_city = path[hops]\n",
    "        next_hops = hops + 1\n",
    "        for (next_city,distance_increment) in connections[current_city]\n",
    "            if !visited(next_city,hops,path)\n",
    "                path[next_hops] = next_city\n",
    "                next_distance = current_distance + distance_increment\n",
    "                if next_distance < min_distance\n",
    "                    return tsp_dist_impl(connections,next_hops,path,next_distance,min_distance,max_hops,jobs_chnl,ftr_result)\n",
    "                end\n",
    "            end\n",
    "        end \n",
    "    else\n",
    "        if jobs_chnl !== nothing\n",
    "            put!(jobs_chnl,(;hops,path,current_distance))\n",
    "        end\n",
    "    end\n",
    "    min_distance\n",
    "end\n",
    "\n",
    "function tsp_dist(connections,city)\n",
    "    max_hops = 2\n",
    "    num_cities = length(connections)\n",
    "    path=zeros(Int,num_cities)\n",
    "    hops = 1\n",
    "    path[hops] = city\n",
    "    current_distance = 0\n",
    "    min_distance = typemax(Int)\n",
    "    jobs_chnl = RemoteChannel(()->Channel{Any}(10))\n",
    "    ftr_result = @spawnat 1 (;path,min_distance_ref=Ref(min_distance))\n",
    "    task = @async begin\n",
    "        tsp_dist_impl(connections,hops,path,current_distance,min_distance,max_hops,jobs_chnl,nothing)\n",
    "        for w in workers()\n",
    "            put!(jobs_chnl,nothing)\n",
    "        end\n",
    "    end\n",
    "    @sync for w in workers()\n",
    "        @spawnat w begin\n",
    "            max_hops = typemax(Int)\n",
    "            jobs_channel = nothing\n",
    "            while true\n",
    "                job = take!(jobs_chnl)\n",
    "                if job == nothing\n",
    "                    break\n",
    "                end\n",
    "                hops = job.hops\n",
    "                path = job.path\n",
    "                current_distance = job.current_distance\n",
    "                tsp_dist_impl(connections,hops,path,current_distance,min_distance,max_hops,jobs_channel,ftr_result)\n",
    "            end\n",
    "        end\n",
    "    end \n",
    "    result = fetch(ftr_result)\n",
    "    (;path = result.path, distance = result.min_distance_ref[])\n",
    "end\n",
    "city = 1\n",
    "tsp_dist(connections,city)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "370a1205",
   "metadata": {},
   "outputs": [],
   "source": []
  }
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