Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2001
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2001

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Re: Problem with FourierTransform

  • To: mathgroup at smc.vnet.net
  • Subject: [mg30367] Re: [mg30349] Re: Problem with FourierTransform
  • From: BobHanlon at aol.com
  • Date: Sun, 12 Aug 2001 02:29:55 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

In a message dated 2001/8/11 4:27:07 AM, 
oliver.friedrich at tz-mikroelektronik.de writes:

>Sorry, I did a writing error, the following is the correct input. So take
>look, regard the phase shift b and d
>
>FourierTransform[Cos[a t+b]*Cos[c t+d],t,f]
>works fine
>
>
>FourierTransform[Cos[a t]*Cos[c t+d],t,f]
>works fine
>
>FourierTransform[Cos[a t+b]*Cos[c t],t,f]
>works fine
>
>FourierTransform[Cos[a t]*Cos[c t],t,f]
>doesn't work at all
>
>Any ideas?
>

Evaluates on my system

$Version

"4.1 for Power Macintosh (November 2, 2000)"

(FourierTransform[Cos[a t+b]*Cos[c t+d],t,f] /. {b -> 0, d -> 0})== 
  FourierTransform[Cos[a t]*Cos[c t],t,f]

True

You might try using TrigReduce prior to transforming

Factor[FourierTransform[TrigReduce[Cos[a t] Cos[c t]],t,f]]

(1/2)*Sqrt[Pi/2]*(DiracDelta[a - c - f] + 
   DiracDelta[a + c - f] + DiracDelta[a - c + f] + 
   DiracDelta[a + c + f])


Bob Hanlon
Chantilly, VA  USA


  • Prev by Date: Re: Expanding Trig Power Identities
  • Next by Date: Re: Hiding parts of a graph
  • Previous by thread: Re: Problem with FourierTransform
  • Next by thread: No Page Break in Group?