def print_matrix(start, width, height):
    """
    Prints a matrix of numbers width columns 'wide' and 'height' columns high.
    The top-left entry is equal to 'start'. Keeping the row constant, numbers
    increase by one as we move bone column left. Keeping the column constant,
    numbers increase by 'width' as we move one row down.
       width, height: int > 0
       start: int
    
    Sample output for start=10, width=3, height=3:

    10 11 12
    13 14 15
    16 17 18
    
    """
    num = start
    for row in range(height):
        for col in range(width):
            # use the tab character '\t' to evenly space out columns
            #  (remove the + '\t' to see what happens)
            print str(num) + '\t',
            num += 1
        print