Search All of the Math Forum:

Views expressed in these public forums are not endorsed by NCTM or The Math Forum.

Notice: We are no longer accepting new posts, but the forums will continue to be readable.

Topic: Help with finding zeros
Replies: 7   Last Post: Sep 14, 2010 3:35 PM

 Messages: [ Previous | Next ]
 Bob Adams Posts: 55 Registered: 12/13/04
Re: Help with finding zeros
Posted: Sep 13, 2010 11:37 AM

On Sep 13, 10:01 am, "Rod" <rodrodrod...@hotmail.com> wrote:
> "Greg Neill" <gneil...@MOVEsympatico.ca> wrote in message
>
> news:BUpjo.55715\$iw4.28826@unlimited.newshosting.com...
>
>
>
>
>

> >> I could use a little help trying to solve the following engineering
> >> problem (no, I am not a student looking for homework help!)

>
> >> I need to find the values of w which cause the following summation to
> >> go to zero

>
> >> sum (n = 1 to N) of exp(-i*w*ln(n))
>
> >> where i is the usual sqrt(-1)
>
> >> For a given N, there are infintely many solutions due to the
> >> periodicity of exp(-i ...)
> >> How do I find these solutions?

>
> >> Thanks for any pointers.
>
>
> > Have you looked into expanding the exponentials into
> > trig form?  You'll then have a sum of cos and
> > imaginary sin terms which will each have to sum to
> > zero separately.

>
> That's my approach as well
> Wouldn't w have to be complex to achieve both series being zero.
>
> Is this not a truncated zeta function?- Hide quoted text -
>
> - Show quoted text -

Yes, this is related to the zeta function.

I was hoping to to find a solution where w is real, but this may not
be possible as you point out

Bob

Date Subject Author