Re: How to construct symmetric matrix from just a one half matrix

• To: mathgroup at smc.vnet.net
• Subject: [mg110390] Re: How to construct symmetric matrix from just a one half matrix
• From: "Nasser M. Abbasi" <nma at 12000.org>
• Date: Wed, 16 Jun 2010 05:39:12 -0400 (EDT)
• References: <hv76li\$k4j\$1@smc.vnet.net>
• Reply-to: nma at 12000.org

```On 6/14/2010 11:30 PM, dragec wrote:
> please help me with simple to apply function that will construct
> symmetric matrix from given just a half matrix with diagonal.
> Eg:
>
> From:
> 1  0  0  0
> 2  3  0  0
> 4  9  5  0
> 2  2  3  4
>
> To give:
>
> 1  2  4  2
> 2  3  9  2
> 4  9  5  3
> 2  2  3  4
>

one way:

a = {{1, 0, 0, 0},
{2, 3, 0, 0},
{4, 9, 5, 0},
{2, 2, 3, 4}};

Transpose[LowerTriangularize[a, -1]] + a

{{1, 2, 4, 2},
{2, 3, 9, 2},
{4, 9, 5, 3},
{2, 2, 3, 4}
}

--Nasser

```

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