public double getDouble(long... coordinates) {
   if (inv == null) {
     DenseMatrix A = new MTJDenseDoubleMatrix2D(getSource()).getWrappedObject();
     DenseMatrix I = Matrices.identity((int) getSource().getColumnCount());
     DenseMatrix AI = I.copy();
     inv = new MTJDenseDoubleMatrix2D((DenseMatrix) A.solve(I, AI));
   }
   return inv.getAsDouble(coordinates);
 }