[Boost-bugs] [Boost C++ Libraries] #4441: SFINAE for operator * breaking auto differentiation code

Subject: [Boost-bugs] [Boost C++ Libraries] #4441: SFINAE for operator * breaking auto differentiation code
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2010-07-15 22:16:34

#4441: SFINAE for operator * breaking auto differentiation code
------------------------------------------------+---------------------------
 Reporter:  Jesse Perla <jesseperla@…>          |       Owner:  guwi17 
     Type:  Bugs                                |      Status:  new    
Milestone:  Boost 1.44.0                        |   Component:  uBLAS  
  Version:  Boost 1.44.0                        |    Severity:  Problem
 Keywords:                                      |  
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 A while back we had discussed adding overload resolution with SFINAE to
 the matrix/vector expressions involving scalars in order to implement
 operator*, etc.
 The choice was made to use is_convertible between the scalar and matrix
 type.

 But this ended up breaking an auto-differentiation library (CPPAD) I was
 using.  Templated AD libraries will often have their own, arithmetic type
 which will record operations of the type * a double, etc. for a matrix
 multiplication by a scalar, etc. But you can't convert between them!

 The basic change is to change from using is_convertible to using
 is_arithmetic.  A change to the result type is also needed for
 autodifferentation to work.

 See the attached patch for the change to matrix/vector expression.

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Ticket URL: <https://svn.boost.org/trac/boost/ticket/4441>
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