code: public static void addColTimes(Matrix matrix, long diag, long fromRow, long col, double factor) {
  		long rows = matrix.getRowCount();
  		for (long row = fromRow; row < rows; row++) {
  			matrix.setAsDouble(
  					matrix.getAsDouble(row, col) - factor * matrix.getAsDouble(row, diag), row, col);
  		}
  	}
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