How to adjust the width in Vim?

I want to use the vsplit command in Vim, and let the left and right part of window have different width,
for example, the left window is more wide than the right,
what should I do?  I mean, which short key can help do that. 

I know, ctrl w +  and ctrl w - can adjust the height of current window.  
But how to adjust the width?    

Thanks in advance.

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