Re: Vector multiplication??

*To*: mathgroup at yoda.physics.unc.edu*Subject*: Re: Vector multiplication??*From*: "Paul N. Schatz" <pns at fermi.clas.virginia.edu>*Date*: Wed, 2 Dec 92 14:14:50 -0500

On Nov 29, 15:48, "Katherine (Williams) Derbyshire" wrote: > Subject: Vector multiplication?? > I have an arbitrary vector > A = Array[a,3] = {a[1], a[2], a[3]} > > The dot product of this vector with itself, is evaluated correctly by > Mathematica: > a[1]^2 + a[2]^2 + a[3]^2 > > The 'ordinary' product of this vector with itself, A^2, should be > equivalent to the dot product. It is, in fact, conventional in > mechanical engineering to interpret A^2 as the square of the magnitude > of A, (i. e. as a dot product). My linear algebra text doesn't offer > any definition for this expression at all. Unfortunately, Mathematica > (2.0 for Windows) interprets A^2 as > {a[1]^2, a[2]^2, a[3]^2} > which isn't the same at all. > > What's going on here? I know I could fix this by writing a > transformation rule, but it would be nice if Mathematica didn't give > wrong answers in the first place. > -- > Katherine (Williams) Derbyshire > kewms at kew.com > > Are we having fun, yet? > > -- End of excerpt from "Katherine (Williams) Derbyshire" <kewms at kew.com> I would like to point out that this is NOT a wrong answer. The product in question is called the Hadamard product. It in fact is EXCEEDINGLY useful in many Mathematica applications. -- Paul N. Schatz Chemistry Department University of Virginia McCormick Road Charlottesville, VA 22901, USA phone: 804-924-3249 email: pns at virginia.edu