Re: Set diagonal of square matrix
- To: mathgroup at smc.vnet.net
- Subject: [mg117076] Re: Set diagonal of square matrix
- From: Ray Koopman <koopman at sfu.ca>
- Date: Wed, 9 Mar 2011 06:58:56 -0500 (EST)
- References: <ikt5e6$t68$1@smc.vnet.net> <ikvohg$f4u$1@smc.vnet.net>
On Mar 6, 2:44 am, Ray Koopman <koop... at sfu.ca> wrote:
> On Mar 5, 3:05 am, Szabolcs <szhor... at gmail.com> wrote:
>
>> Dear MathGroup members,
>>
>> Is there any simple way to set the diagonal of a square matrix to a
>> vector (of appropriate length)? Of course there are ways to do it,
>> but I was wondering if there was a simple, one-line way.
>
> ReplacePart[{{0,0,0}, {0,0,0}, {0,0,0}}, {i_,i_} :> {a,b,c}[[i]] ]
>
> {{a,0,0}, {0,b,0}, {0,0,c}}
A pre- version 6 equivalent of
ReplacePart[matrix, {i_,i_} :> vector[[i]] ]
would be
With[{r = Range@Length@matrix},
ReplacePart[matrix, vector, {#,#}&/@r, List/@r ]]