如何在ruby中设置二维数组的元素？

I tried:

我试过了：

1.9.3-p448 :046 > a=Array.new(7){Array.new(7)}
 => [[nil, nil, nil, nil, nil, nil, nil], 
     [nil, nil, nil, nil, nil, nil, nil], 
     [nil, nil, nil, nil, nil, nil, nil], 
     [nil, nil, nil, nil, nil, nil, nil], 
     [nil, nil, nil, nil, nil, nil, nil], 
     [nil, nil, nil, nil, nil, nil, nil], 
     [nil, nil, nil, nil, nil, nil, nil]]
1.9.3-p448 :047 > a[0,0]='a'
 => "a" 
1.9.3-p448 :048 > a[0,1]='b'                                                                
 => "b" 
1.9.3-p448 :049 > a[0,2]='c'                                                                
 => "c"
1.9.3-p448 :050 > a[1,0]='d'                                                                
 => "d" 
1.9.3-p448 :051 > a[1,1]='e'                                                                
 => "e" 
1.9.3-p448 :052 > a[1,2]='f'                                                                
 => "f" 
1.9.3-p448 :046 > a=Array.ne