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Im implementing 2 algorithms for the TSP which uses a class which includes the routes, their cost, etc. At the minute it uses random values which is fine, although I now need to compare the algorithms so to make this fair I need to make the inputs the same (which is obviously unlikely to happen when using random inputs!) The issue im having is I dont know how to change it from random values to inserting pre-determined values into the 2D array, not just that but I also dont know how to calculate the costs of these values.

Randomly generates node values:

Random rand = new Random();
            for (int i=0; i<nodes; i++) {
                for (int j=i; j<nodes; j++) {
                    if (i == j)
                        Matrix[i][j] = 0;
                    else {
                        Matrix[i][j] = rand.nextInt(max_distance);
                        Matrix[j][i] = Matrix[i][j];
                    }
                }
            }

Im assuming for the above a declare a matrix of say [4][4] and then int matrix [][] = insert values ?

I do not help with some other sections of this class but I think I need to make sure this part is right before asking anymore!

Thanks a lot in advance!

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why don't you just keep using random values, but the same values for both algorithms in each run? – HericDenis Jan 14 at 16:25
Just in case, you are interested in initialising a 2D array, manually : egle.lanet.lv/javafaq/course/week2/33.html – TJ- Jan 14 at 16:25
read values from file – Nikolay Kuznetsov Jan 14 at 16:29

2 Answers

up vote 2 down vote

You could set a seed instead for each random number generator therefore guaranteeing that for each implementation you test, the same sequence of pseudo-random numbers is being created.

This would save the effort of manually entering lots of values.

Edit to show seed method:

Random r = new Random(56);

Every time r is created with the seed of 56 it will produce the exact same sequence of random numbers. Without a seed I believe the seed is defaulted to the system time (giving the illusion of truly random numbers).

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Thanks for the reply, how do I go about setting a seed? Its something ive never heard of before but if it saves time and effort im more than up for it! Thank you – thrash Jan 14 at 16:39
@user1886061 updated my answer to give an example. – Jon Taylor Jan 14 at 16:41
up vote 2 down vote

you can do initialization of 2D array like this:

    double matrix[][] = { { v1, v2, ..., vn }, { x1, x2, ..., xn }, ..., { y1, y2, ..., yn } };

where each inner {} represents the outter (first) index and each inner element represents the innermost (second) intex.

Example: to acess element x1 you do this:

    matrix[1][0];

This is the answer that you asked for, but I still think that it's better to use the same set of random values for both algorithms, Jon Taylor showed a good way for doing that. The code to set the seed looks like this:

    int seed = INTEGER_VALUE;
    Random rand = new Random(seed);

this way you will ever get the same set of values.

share|improve this answer
Thanks a lot for that, I think I was implementing it correctly when I tried it before coming on here then. I have another few instances of the matrix referred to in the code too but im not sure whether it needs to be changed? It also seems quite complicated to constantly find the difference between the values in the matrix, would you agree? – thrash Jan 14 at 16:38
Well, let me fully understand what you want to ask, why would you need to change the matrix reference? Like, if you change any value of the matrix using say, reference variable matrix1, all changes will be exactly equal using another reference variable matrix2, if they refer to the same object as I think it does in your case. If this is not the answer please be clear. And when you talk about differences between two matrices or diffeces into the same matrix? – HericDenis Jan 14 at 16:43

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