Re: [boost] [ublas] bugfix for matrix operation /

Subject: Re: [boost] [ublas] bugfix for matrix operation /
From: Mario Mulansky (mario.mulansky_at_[hidden])
Date: 2013-04-17 12:13:24

On Wednesday, April 17, 2013 09:06:35 AM Jeffrey Lee Hellrung, Jr. wrote:
> On Wed, Apr 17, 2013 at 7:08 AM, Mario Mulansky 
<mario.mulansky_at_[hidden]>wrote:
> > On Tuesday, April 16, 2013 08:16:57 PM Steven Watanabe wrote:
> > > AMDG
> > > 
> > > On 04/16/2013 07:20 PM, Mario Mulansky wrote:
> > > > Hi,
> > > > 
> > > > I wanted to add an elementwise divide operations for ublas matrices
> > 
> > using
> > 
> > > > operator /
> > > 
> > > I don't think that's such a great idea.
> > > Using regular operators for elementwise
> > > operations is likely to be surprising.
> > > i.e.  if you can do (A / B) you should
> > > be able to do (A * B) as well, and it
> > > you be the inverse of A / B.  But
> > > multiplication is defined for matrices
> > > and is *not* an elementwise operation.
> > > There is no way to define this that
> > > won't surprise someone.  There's a
> > > good reason why uBlas doesn't provide
> > > these operators already and why MATLAB
> > > has a separate set of operators for
> > > elementwise operations.
> > 
> > uh wait, i dont want to add this operator to ublas. I need it within
> > odeint
> > and it would be part of some ublas_extension.hpp in odeint, it would be
> > merely
> > an implementation detail no user would encounter.
> 
> [...]
> 
> If no user would encounter it, why don't you just define and use a free
> function elementwise_divide? Why does it have to be named operator/?

oh because then i can reuse my code that is based on operator / being defined, 
it's just the easier way for me to go.

but despite that i consider it a bug in ublas. the templated operator 
matrix/skalar gets instantiated even if i write matrix/matrix. this then 
results in a nasty compiler error instead of telling me operator/ for matrix 
matrix is not defined, as it would if the enable_if was there.

best,
mario

> 
> - Jeff
> 
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