Re: FindRoot for the determinant of a matrix with a varying size
- To: mathgroup at smc.vnet.net
- Subject: [mg59739] Re: FindRoot for the determinant of a matrix with a varying size
- From: Peter Pein <petsie at dordos.net>
- Date: Fri, 19 Aug 2005 04:32:09 -0400 (EDT)
- References: <de13n4$8so$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Wonseok Shin schrieb:
> Hello everyone,
>
> I am a user of Mathematica 5.1 for Mac .
> I defined the function using the determinant of a matrix of a varying
> size. Even though this function is well-behaving, it seems that
> FindRoot cannot deal this function. Please look at the following code:
>
> -------------------------------------------------
> In[1]:=
> f[x_] := Det[Table[Exp[(i - j)/x]/x , {i, 2, 5, x}, {j, 2, 5, x}]]
>
> In[2]:=
> Plot[f[x], {x, 3, 30}]
> -------------------------------------------------
>
> By running the above Plot command, you can see clearly that the
> function f is very smooth in the interval 3< x < 30, and f[x] == 0.1
> has a solution in 5 < x < 15.
>
> But I've failed to find a solution of f[x] == 0.1 using FindRoot:
>
> -------------------------------------------------
> In[3]:=
> FindRoot[f[x] == 0.1, {x, 5}]
>
> Table::iterb : Iterator {i, 2, 5, x} does not have appropriate bounds.
> -------------------------------------------------
>
> Is there any workaround for this problem?
>
> Thanks,
>
> Wonseok Shin
>
Hi,
by construction, f[x]==1/x for x > 3. So f[10]==1/10.
But if you want to use your definition, use f[x_?NumericQ]:=Det[...].
Peter
--
Peter Pein
Berlin