MathGroup Archive 1998

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

Search the Archive

Re: No trace of trace!

  • To: mathgroup at smc.vnet.net
  • Subject: [mg15140] Re: No trace of trace!
  • From: David Annetts <dannetts at laurel.ocs.mq.edu.au>
  • Date: Wed, 16 Dec 1998 03:11:15 -0500
  • Organization: CRCAMET/Macquarie University
  • References: <754ulc$je8@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi Peter,

> 
> So I'm doing my QFT homework, and I need to know what the matrices A and
> B would look like if
> 
>     Tr[A] Tr[B] = Tr[AB]
> 
> were true.  (For example, it's true if A=B=1 or if A=-B=1).  I quickly
> walk over to my computer desk, sit down and power up Mathematica.  I
> enter two  matrices and type Trace[A] and got wierd output.
> 
> So I go to help and find out Trace is not a matrix operation.
> 
> After looking for close to 5 minutes, I've concluded that the Trace
> *matrix* operation is either not present or well hidden.
> 
> Can someone tell me which one?

   From the Online help in version 3.0 ...

"You can get the trace of the matrix by explicitly constructing a sum of
the elements on its leading diagonal. "

eg Sum[ m[[i, i]], {i, 2} ] where m = {{a, b}, {c, d}}

It's in Section 3.7.7: Basic Matrix operations.

-- 
 ==================================================================
 David Annetts                                       _____________
 http://www.ocs.mq.edu.au/~dannetts/                |C R C A M E T|
                                                    |-------------|
                                                    |_____        |
 CRC for Australian Mineral                         |````` \      |
 Exploration Technologies                           |`````/$\     |
 Earth Sciences                                     |````/$$$\____|
 Macquarie University, NSW 2109                     |```/$$$/.....|
 AUSTRALIA                                          |``/$$$/......|
 phone: +(1-61-2) 9850 9280, fax (1-61-2) 9850 8366  -------------
 ==================================================================


  • Prev by Date: Pure Functions
  • Next by Date: help
  • Previous by thread: No trace of trace!
  • Next by thread: Re: No trace of trace!