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Re: sparse matrix question

• To: mathgroup at smc.vnet.net
• Subject: [mg56155] Re: sparse matrix question
• From: Peter Pein <petsie at arcor.de>
• Date: Sun, 17 Apr 2005 03:06:59 -0400 (EDT)
• References: <d3lrsq$sef$1@smc.vnet.net> <200504150847.EAA11518@smc.vnet.net> <d3qh7j$odd$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Ted Sariyski wrote:
> Hi,
> 
> I have a list
> l={{a,b},{c,d},{e,f}}
> and a list of pointers  to the non-zero columns of a 
> sparse matrix e.g. p={3,4,6}:
>       
>       | 0 0 a c 0 d 0 ... |
> m=    |                   |
>       | 0 0 b d 0 e 0 ... |
> 
> What is the best way to do this? How can I address a column in 
> mathematica?
> 
> Thanks,
> Ted
> 
> 
> 
> 
m = {{0, 0, 0, a, c, 0, d, 0, andsoon},
     {0, 0, 0, b, d, 0, e, 0, more}};
In[2]:= m[[All,4]]
Out[2]= {a, b}
In[3]:= m[[All,#]]& /@ Range[Min[Length /@ m]]
Out[3]= {{0, 0}, {0, 0}, {0, 0}, {a, b},
  {c, d}, {0, 0}, {d, e}, {0, 0},
  {andsoon, more}}

-- 
Peter Pein
Berlin

• References:
  • Re: Wierd problems with Mathematica - inversion of a 12x12 matrix
    • From: David Bailey <dave@Remove_Thisdbailey.co.uk>