Printing to screen a matrix or data.frame in one chunk (not splitting columns)

Hello,

I saw this nice trick I want to replicate but I lost the source and  
I hope
one of you can point me to the solution.  My problem is that I don't  
know
the correct words to query this.

When I print to screen a matrix or data.frame the columns are split  
and
printed below the previous ones; even though I have plenty of screen  
left.

E.g.,

my_matrix = matrix(runif(30),nrow=3,ncol=10)
my_matrix

         [,1]      [,2]      [,3]       [,4]      [,5]      [,6]
[,7]
[1,] 0.4979305 0.1155717 0.4484069 0.29986049 0.5427566 0.4324351
0.269171456
[2,] 0.8405987 0.3605237 0.6615507 0.75305248 0.8569482 0.3401004
0.192526423
[3,] 0.5608779 0.3953941 0.9995035 0.03141064 0.7985053 0.4903582
0.000490054
         [,8]      [,9]      [,10]
[1,] 0.1402751 0.2852381 0.98816751
[2,] 0.8337806 0.7322920 0.17505541
[3,] 0.5414113 0.4668012 0.04420137

So there is a way to resize the space for printing so that  
everything in
printed in one chunk.

Thanks in advance,
Adrian