code: public static void swapCols(double[][] matrix, int col1, int col2) {
  		double temp = 0;
  		int rows = matrix.length;
  		double[] r = null;
  		for (int row = 0; row < rows; row++) {
  			r = matrix[row];
  			temp = r[col1];
  			r[col1] = r[col2];
  			r[col2] = temp;
  		}
  	}
docs: Swap components in the two columns.
  
  @param matrix
  the matrix to modify
  @param col1
  the first row
  @param col2
  the second row