Matrix multiplication using EJML

Question

double[][] data_array
SimpleMatrix dataMatrix = new SimpleMatrix(data_array);
SimpleMatrix omegaMatrix = new SimpleMatrix(omega);
SimpleMatrix cMatrix =  dataMatrix.mult(omegaMatrix);
System.out.println("Multiplied");
cMatrix.print();

I am using EJML library for matrix operation.

1.How to convert a simple matrix back to double[][].

The above result is a 1 by 1 matrix.

2. Can we store this value in a double variable?

Answer 1

The data is not necessarily stored as a double[][] array. In fact, it is stored as a double[] array. You can obtain the internal DenseMatrix64F, and from this, you can obtain the double[] array:

double data[] = cMatrix.getMatrix().getData();

This array stored the data in row-major format.

In order to store this in a single value, you can call

double singleValue = cMatrix.getMatrix().getData()[0];

---

EDIT: I think this was asked for in the comments, but I'm not sure....:

private static double[][] toArray(DenseMatrix64f matrix) 
{
    double array[][] = new double[matrix.getNumRows()][matrix.getNumCols()];
    for (int r=0; r<matrix.getNumRows(); r++)
    { 
        for (int c=0; c<matrix.getNumCols(); c++)
        {
            array[r][c] = matrix.get(r,c);
        }
    }
    return array;
}