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Re: Function construction and also symmetric matrices

  • To: mathgroup at smc.vnet.net
  • Subject: [mg109526] Re: Function construction and also symmetric matrices
  • From: "Kurt TeKolste" <tekolste at fastmail.net>
  • Date: Mon, 3 May 2010 07:53:22 -0400 (EDT)
  • References: <hnva64$88k$1@smc.vnet.net>

Or, even better,

randomSymmetricMatrix2[dimension_Integer] := Module[{a},
  a = PadRight[#, dimension] & /@ 
    Table[RandomReal[], {row, dimension}, {column, row - 1}];
  a + a\[Transpose] + IdentityMatrix[dimension]]

ekt

On Sun, 02 May 2010 22:52 -0400, "Kurt TeKolste" <tekolste at fastmail.net>
wrote:
> How about this?
> 
> randomSymmetricMatrix[dimension_Integer] := Module[{a=
>  Table[Join[ConstantArray[0, (i - 1)], {1/2}, 
>    Table[RandomReal[], {k, dimension - i}]], {i, dimension}]},
>    a+Transpose[a]]
> 
> On Wed, 24 Mar 2010 04:40 -0500, "Diamond, Mark" <dot at dot.dot> wrote:
> > Brilliant. Thank you, both Raffy and Ray.
> >
> >
> > "Ray Koopman" <koopman at sfu.ca> wrote in message
> > news:ho76uf$sm$1 at smc.vnet.net...
> > > On Mar 20, 12:46 am, "Diamond, Mark" <d... at dot.dot> wrote:
> > >> Thank you Ray.
> > >>
> > >> Have you any thoughts about the second question?
> > >>
> > >> Cheers, Mark
> > >
> > > In[1]:= makesymat[n_] := ToExpression["symat[" <> ToString@n <> "]
> > > := Function[" <> ToString@Table[ Which[i > j, SequenceForm["#[[",(i-1)(i-
> > > 2)/2 + j,"]]"],     i < j, SequenceForm["#[[",(j-1)(j-2)/2 +
> > > i,"]]"],     True,  "1"], {i,n},{j,n}] <> "]" ]
> > >
> > > In[2]:= makesymat[4]
> > >
> > > In[3]:= ?symat
> > >
> > > Global`symat
> > >
> > > symat[4] := {{1, #1[[1]], #1[[2]], #1[[4]]},            {#1[[1]], 1,
> > > #1[[3]], #1[[5]]},            {#1[[2]], #1[[3]], 1, #1[[6]]},
> > > {#1[[4]], #1[[5]], #1[[6]], 1}} &
> > >
> > > In[4]:= symat[4]@{a,b,c,d,e,f}
> > >
> > > Out[4]= {{1, a, b, d},        {a, 1, c, e},        {b, c, 1, f},
> > > {d, e, f, 1}}
> > >
> >
> >
> >
> >
> 


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