Re: Function construction and also symmetric matrices

*To*: mathgroup at smc.vnet.net*Subject*: [mg109517] Re: Function construction and also symmetric matrices*From*: "Kurt TeKolste" <tekolste at fastmail.net>*Date*: Mon, 3 May 2010 06:11:09 -0400 (EDT)

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}} > > > > > >