code: public static void addRowTimes(double[][] matrix, int diag, int fromCol, int row, double factor) {
  		int cols = matrix[0].length;
  		double[] d = matrix[diag];
  		double[] r = matrix[row];
  		for (int col = fromCol; col < cols; col++) {
  			r[col] -= factor * d[col];
  		}
  	}
docs: Add a factor times one row to another row
  
  @param matrix
  the matrix to modify
  @param diag
  coordinate on the diagonal
  @param fromCol
  first column to process
  @param row
  row to process
  @param factor
  factor to multiply