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