Some operations on matrix

[Christian LeMoussel]

Hi all,

I have a symetric square matrix A.
    double[,] A =
    {
        { 100.00, 27.56, 33.89},
        { 27.56, 100.00, 24.76},
        { 33.89, 24.76, 100.00}
    };
The values ​​in matrix are percentages of similarity between texts.

Without taking the value of the diagonal, I would like to calculate

Average  by line :
Average1 = (27.56 + 33.89) / 2 = 30.73
Average1 = (27.56 + 24.76) / 2 = 26.16
Average3 = (33.89, 24.76) / 2 = 29.33



Total Average :
TotalAverage = (30.73 + 26.16 + 29.33) / 3 = 28.74


Is it possible to calculate these averages with Accord.NET framework?

Regards.

Christian.

[César]

Hi Christian!

Well, you could try computing the mean using Statistics.Tools.Mean and then removing the influence of the diagonal afterwards. Otherwise, you could set the diagonal to zero, compute the sum and divide by the new number of samples. Perhaps something like this might work:

            double[,] a =

            {
                { 100.00, 27.56, 33.89},
                { 27.56, 100.00, 24.76},
                { 33.89, 24.76, 100.00}
            };

            a = a.Subtract(Matrix.Diagonal(3, 100.0));

            var mean = a.Sum().Divide(2);

Hope it helps!

Regards,

Cesar

[Christian LeMoussel]

Thank's for you help César.

With this  square array, I use System.Array.GetLength(int dimension) to get the length of a specific dimension.

var mean = A.Sum().Divide(A.GetLength(0) - 1);