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MathGroup Archive 2004

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Re: Re: Creating a symmetric matrix


It seems that I was the only one who thinks that a "triangular matrix" 
is a "strick triangular matrix", that is with zeros on the diagonal. 
had I not made this assumption I would have suggested:


A+Transpose[A]*Array[KroneckerDelta[#1 != #2,True]&,Dimensions[A]]


Andrzej


On 12 Mar 2004, at 08:02, Andrzej Kozlowski wrote:

>
> On 11 Mar 2004, at 09:50, Mark Coleman wrote:
>
>> Greetings,
>>
>> How can I efficiently build a symmetric matrix from an upper 
>> triangular
>> one, i.e., extract the upper triangular elements and insert them into
>> the lower triangle in such a way as to make the resulting square 
>> matrix
>> symmetric?
>>
>> Thanks,
>>
>> Mark
>>
>>
>>
>
> The most natural way must be
>
> A+Tranpose[A]
>
> e.g.
>
> A = Array[KroneckerDelta[#1 < #2, True] & , {3, 3}];
>
>
> {{0, 1, 1}, {0, 0, 1}, {0, 0, 0}}
>
>
> A + Transpose[A]
>
>
> {{0, 1, 1}, {1, 0, 1}, {1, 1, 0}}
>
>
>
> Andrzej Kozlowski
> Chiba, Japan
> http://www.mimuw.edu.pl/~akoz/
>
>


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