Re: What am i missing?
- To: mathgroup at smc.vnet.net
- Subject: [mg12724] Re: What am i missing?
- From: "Allan Hayes" <hay at haystack.demon.cc.uk>
- Date: Thu, 4 Jun 1998 02:52:10 -0400
- References: <6kvrgi$7td@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Ray Pendergraph wrote in message <6kvrgi$7td at smc.vnet.net>... >Im not saying this is a glitch and I do not want to start a debate like >the one about why the square root of x squared is not x on >Mathematicabut my question is this: Why does Mathematica square each >individual element in a matrix when I say [A]^2 . For instance, I have >an n x n matrix [A] filled with random numbers. Should'nt {A]^2 be the >same as [A].[A] instead of squaring each component of the matrix (which >is what Mathematica does when you say A^2).There must be a reason why >Wolfram did this and I am not exactly a seasoned mathematician so could >someone explain? Ray, It's often useful to have the this entry by entry operation as well as the Dot product, and it follows standard math proctice with lists and vectors a = {p,q,r}; b={x,y,z}; a+b {p + x, q + y, r + z} a/b p q r {-, -, -} x y z a/k p q r {-, -, -} k k k Sin[a] {Sin[p], Sin[q], Sin[r]} In Mathematica it's called "threading", and is done automatically be functions that have the attribute Listable: Attributes[Sin] {Listable,NumericFunction,Protected} ------------------------------------------------------------- Allan Hayes Training and Consulting Leicester UK http://www.haystack.demon.co.uk hay at haystack.demon.co.uk voice: +44 (0)116 271 4198 fax: +44(0)116 271 8642