Re: [eigen] two decisions to take

[Andre Krause <post@xxxxxxxxxxxxxxxx>]

Benoît Jacob wrote:
> On Tuesday 04 September 2007 19:47:18 Schleimer, Ben wrote:
> > I disagree. I think that eigen2 should be using methods instead of global
> > functions because it's a C++ toolkit.
>
> It's not a big deal adding member functions. In Eigen1 we allowed both 
> dot(v,w) and v.dot(w), so I think we'll do the same in Eigen2, since there 
> seems to be strong advocates of both approaches :)

fine, as long as the global dot or cross functions are present (of 
course inside eigen's namespace), i have no objections against member 
functions. if it is well documented that those change the value of the 
object itself.

> FYI I've implemented the matrix-matrix and matrix-vector operator* as a 
> global, and I don't think this is a problem since as Andre said the compiler 
> will resolve that overloading and call this operator* only when appropriate.
>
> > or better:
> >
> > double zLen = x^y*n*3;
> > (the ^ is the cross operator and the * is the dot operator. For vectors not
> > of dim3, ^ should be the wedge operator)
>
> I won't give operator* the additional meaning of dot product. It already has 4 
> meanings (matrix-matrix, matrix-vector, matrix-scalar, vector-scalar 
> products), this is enough!

i had operator* in my own little small veclib as dot product for a long 
time, but now i follow the way blitz++ and tvmet and do NOT give it the 
meaning of a dot-product. there are many good arguments doing so, but i 
forgot them ;-) (somewhere on the blitz++ mailing list)

> I agree with the operator^ for cross product, actually I proposed it one year 
> ago on #eigen for Eigen1 but someone objected. I don't remember what the 
> objection was.
>
> If we go for operator^ for cross product, then I suggest operator| for dot 
> product. This is classical mathematical notation, especially in quantum 
> mechanics (Dirac's "bras" and "kets").

too bad c++ cannot overload the dot-operator... but well, if "|" is that 
well known in quantum mechanics (to be honest, never seen that use, do 
you have some link / pdf showing that?), it sounds fine to overload it 
for dot product.


kind regards, andre!
p.s. i am very excited about the upcoming new eigen! thanks for all your 
efforts, benoit ! i like your way of "keep it as simple as possible". so 
maybe even c++ noobs like me will have a chance to understand the magic 
behind expression templates. or at least get the rough idea.