C++ Neural Networks and Fuzzy Logic by Valluru B. Rao M&T Books, IDG Books Worldwide, Inc. ISBN: 1558515526 Pub Date: 06/01/95 |

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Let us now look at Hopfield and Tank’s approach at solving the TSP.

**Hopfield and Tank Example**

The Hopfield network’s use in solving the traveling salesperson problem is a pioneering effort in the use of the neural network approach for this problem. Hopfield and Tank’s example is for a problem with 10 cities. The parameters used were, *A*_{1}= 500, *A*_{2} = 500, *A*_{3} = 200, *A*_{4} = 500, τ = 1, λ = 50, and *m* = 15. A good solution corresponding to a local minimum for *E* is the expected, if not the best, solution (global minimum). An annealing process could be considered to move out of any local minimum. As was mentioned before, the traveling salesperson problem is one of those problems for which a single approach cannot be found that will be successful in all cases. There isn’t very much guidance as to how to choose the parameters in general for the use of the Hopfield network to solve the traveling salesperson problem.

We present a C++ program for the Hopfield network operation for the traveling salesperson problem. The header file is in the Listing 15.1, and the source file is in the Listing 15.2. A **tsneuron** class is declared for a neuron and a **network** class for the network. The **network** class is declared a friend in the **tsneuron** class. The program follows the procedure described for setting inputs, connection weights, and updating.

**Program Details**

The following is a listing of the characteristics of the C++ program along with definitions and/or functions.

**•**The number of cities, the number of iterations, and the distances between the cities are solicited from the user.**•**The distances are taken as**integer**values. If you want to use real numbers as distances, the type for distance matrix needs to be changed to**float**, and corresponding changes are needed for**calcdist ( )**function, etc.**•****tourcity**and**tourorder**arrays keep track of the cities that have to be covered and the order in which it is to be done.**•**A neuron corresponds to each combination of a city and its order in the tour. The*i*th city visited in the order*j*, is the neuron corresponding to the element*j*+*i***n*, in the array for neurons. Here*n*is the number of cities. The*i*and the*j*vary from 0 to*n*– 1. There are*n*^{2}neurons.**•****mtrx**is the matrix giving the weights on the connections between the neurons. It is a square matrix of order*n*^{2}.**•**An input vector is generated at random in the function**main ( )**, and is later referred to as**ip****•****asgninpt ( )**function presents the input vector**ip**to the network and determines the initial activations of the neurons.**•****getacts ( )**function updates the activations of the neurons after each iteration.**•****getouts ( )**function computes the outputs after each iteration.**la**is used as abbreviation for lambda in its argument.**•****iterate ( )**function carries out the number of iterations desired.**•**findtour ( ) function determines the tour orders of cities to be visited using the outputs of the neurons. When used at the end of the iterations, it gives the solution obtained for the traveling salesperson problem.**•**calcdist ( ) function calculates the distance of the tour in the solution.

**Listing 15.1** Header file for the C++ program for the Hopfield network for the traveling salesperson problem

//trvslsmn.h V. Rao, H. Rao #include <iostream.h> #include <stdlib.h> #include <math.h> #include <stdio.h> #define MXSIZ 11 class tsneuron { protected: int cit,ord; float output; float activation; friend class network; public: tsneuron() { }; void getnrn(int,int); }; class network { public: int citnbr; float pra,prb,prc,prd,totout,distnce; tsneuron (tnrn)[MXSIZ][MXSIZ]; int dist[MXSIZ][MXSIZ]; int tourcity[MXSIZ]; int tourorder[MXSIZ]; float outs[MXSIZ][MXSIZ]; float acts[MXSIZ][MXSIZ]; float mtrx[MXSIZ][MXSIZ]; float citouts[MXSIZ]; float ordouts[MXSIZ]; network() { }; void getnwk(int,float,float,float,float); void getdist(int); void findtour(); void asgninpt(float *); void calcdist(); void iterate(int,int,float,float,float); void getacts(int,float,float); void getouts(float); //print functions void prdist(); void prmtrx(int); void prtour(); void practs(); void prouts(); };

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Copyright © IDG Books Worldwide, Inc.

C++ Neural Networks and Fuzzy Logic

ISBN: 1558515526

EAN: 2147483647

EAN: 2147483647

Year: 1995

Pages: 139

Pages: 139

Authors: Valluru B. Rao, Hayagriva Rao

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