3
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?
USB
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1 Answers1

5

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;
}
Marco13
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  • How to take value in double array? – USB Mar 21 '14 at 07:51
  • @SreeVeni The question is not clear. If you're asking for `double value = array[i];` you should read http://docs.oracle.com/javase/tutorial/java/nutsandbolts/arrays.html – Marco13 Mar 21 '14 at 15:33
  • what i was trying to ask is In JAMA, we can convert the Matrix back to double[][].by using double[][] Inverse = PInverse.getArray();Whether we can go like this in EJML – USB Mar 22 '14 at 03:59