Re: assignment of matrix elements
- To: mathgroup at smc.vnet.net
- Subject: [mg17245] Re: assignment of matrix elements
- From: jf alcover <jfalcover at cepme.fr>
- Date: Fri, 30 Apr 1999 02:34:37 -0400
- Organization: cepme
- References: <7g0r8r$dsc@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
this is what i suggest :
In[1]:=mat = Array[m, {4,4}];
v = {{1,2},{1,3},{2,3},{3,1}};
w = {1,5,-2,1};
In[2]:=assign[{x_,y_},z_]:=(mat[[x,y]]=z);
Thread[assign[v,w]];
In[3]:=mat
Out[3]:={{m[1,1],1,5,m[1,4]},{m[2,1],m[2,2],-2,m[2,4]},{1,m[3,2],m[3,3],m[3,4]},{
m[4,1],m[4,2],m[4,3],m[4,4]}}
regards,
Richard Finley wrote:
> This seems like it should be straightforward but I am too tired to think
> about it anymore:
>
> If you have a matrix say mat = Array[m, {4,4}]
>
> and a list of indices say v = {{1,2},{1,3},{2,3},{3,1}}
> with another list of the same length giving the values of the matrix
> elements at
> those indices: w = {1,5,-2,1}
>
> How do you assign values to the matrix elements with those values...ie
> so
> that m[1,2]=1, m[1,3]=5 etc...
>
> Obviously you can do it individually by simple assignment:
> m{1,2]=1
>
> That won't work for me because there are thousands of elements...the
> techniques I have tried so far
> have not worked...any help is greatly appreciated.
>
> Thanks
>
> Richard Finley