docs: public static void addEquals(DMatrixD1 a , double beta, DMatrixD1 b )
      {
          if( a.numCols != b.numCols || a.numRows != b.numRows ) {
              throw new MatrixDimensionException("The 'a' and 'b' matrices do not have compatible dimensions");
          }
  
          final int length = a.getNumElements();
  
          for( int i = 0; i < length; i++ ) {
              a.plus(i, beta * b.get(i));
          }
      }