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 | | From: | Pradeep Aggarwal | | Subject: | Assigning values to a matrix at position specified by a vector | | Date: | Sun, 23 Jan 2005 13:25:56 -0500 |
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 | Hi,
I hope someone might be able to help me out with the
following problem I am facing:
I have a matrix A (e.g. A=zeros(4,4);)
and a vector b (e.g. b=[2 3];)
Now I want to put some value, say 80 in A, at the position given by
b. (i.e. I want A(2,3)=80;).
How do I do this. Please note the fact that the dimension
of A and b are not fixed, and can take any (mutually compatible)
value. That rules out using -- A(b(1), b(2))=80
Thanks in advance.
Pradeep
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| | From: | Mike Nospam | | Subject: | Re: Assigning values to a matrix at position speci | | Date: | Sun, 23 Jan 2005 18:57:13 -0500 |
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| One way to do it is the sparse command:
>> b=[2 3; 1 4; 5 1;6 2]
b =
2 3
1 4
5 1
6 2
>> s=rand(4,1)
s =
0.9501
0.2311
0.6068
0.4860
>> A=full(sparse(b(:,1),b(:,2),s))
A =
0 0 0 0.2311
0 0 0.9501 0
0 0 0 0
0 0 0 0
0.6068 0 0 0
0 0.4860 0 0
Pradeep Aggarwal wrote:
>
>
> Hi,
>
> I hope someone might be able to help me out with the
> following problem I am facing:
>
> I have a matrix A (e.g. A=zeros(4,4);)
> and a vector b (e.g. b=[2 3];)
>
> Now I want to put some value, say 80 in A, at the position given by
> b. (i.e. I want A(2,3)=80;).
>
> How do I do this. Please note the fact that the dimension
> of A and b are not fixed, and can take any (mutually compatible)
> value. That rules out using -- A(b(1), b(2))=80
>
> Thanks in advance.
>
> Pradeep
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