Hi,

I'm porting libmv to Windows and having problems with using Eigen, would appreciate help:

This is HStack() definition from libmv (horizonally stack matrices)

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template
Eigen::Matrix
HStack(const Eigen::Matrix  &left,
       const Eigen::Matrix &right) {

ROWS/COLS are macros for "Dynamic":

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#define COLS
  ((ColsLeft == Eigen::Dynamic || ColsRight == Eigen::Dynamic)
   ? Eigen::Dynamic : (ColsLeft + ColsRight))

#define ROWS
  ((RowsLeft == Eigen::Dynamic && RowsRight == Eigen::Dynamic)
   ? Eigen::Dynamic
   : ((RowsLeft == Eigen::Dynamic)
      ? RowsRight
      : RowsLeft
     )
  )

It works well if both arguments are Eigen::Matrix. Then they have

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HStack(R, t)

t is Vector3d.

MS VC complains:

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1>L:tmplibmv-devellibmv-1srclibmv/multiview/test_data_sets.h(63) : error C2784: 'Eigen::Matrix libmv::HStack(const Eigen::Matrix &,const Eigen::Matrix &)' : [b]could not deduce template argument[/b] for 'const Eigen::Matrix &' from 'libmv::Vec3'

"libmv::Vec3" is defined as "typedef Eigen::Vector3d Vec3;"

Any help would be greatly appreciated.

Seems like I solved it myself.

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template
MatrixBase HStack(MatrixBase& lhs, MatrixBase& rhs)
{
   Derived1 res;
   res << l, r;
   return res;
};

Yep, good solution You may want to make the return type Derived1 automatically determined from Derived2 and Derived3, though.

>You may want to make the return type Derived1 automatically determined from Derived2 and Derived3, though.

That's interesting. How do I do that?

bomboze wrote:>You may want to make the return type Derived1 automatically determined from Derived2 and Derived3, though.

That's interesting. How do I do that?

Something along these lines:

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template
struct hstack_return
{
  typedef typename Derived1::Scalar Scalar;
  enum { RowsAtCompileTime = Derived1::RowsAtCompileTime,
         ColsAtCompileTime = Derived1::ColsAtCompileTime + Derived2::ColsAtCompileTime,
         Options = Derived1::Options,
         MaxRowsAtCompileTime = Derived1::MaxRowsAtCompileTime,
         MaxColsAtCompileTime = Derived1::MaxColsAtCompileTime + Derived2::MaxColsAtCompileTime
  };
  typedef Matrix type;
};

template
typename hstack_return::type
HStack(MatrixBase& lhs, MatrixBase& rhs)
{
  typename hstack_return::type res;
  res << l, r;
  return res;
}


bjacob wrote:Something along these lines:

Awesome! That works. Except for my typo in original code that should be: "res << lhs, rhs;" (instead of l,r)

Thanks!

Thanks once again for the solution, Benoît, I'm growing to really love Eigen.

However I've wanted to push the things a little further and stumbled into something I don't understand about Eigen's lazy evaluation.

I've implemented HStack as operator| (VStack as operator&), so that I can do "(A|B)", but when I do "(A*B)|C" I get:

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'Options' : is not a member of 'Eigen::Product'

in here:

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  enum { RowsAtCompileTime = Derived1::RowsAtCompileTime,
         ColsAtCompileTime = Derived1::ColsAtCompileTime + Derived2::ColsAtCompileTime,
>>>         Options = Derived1::Options,
         MaxRowsAtCompileTime = Derived1::MaxRowsAtCompileTime,
         MaxColsAtCompileTime = Derived1::MaxColsAtCompileTime + Derived2::MaxColsAtCompileTime


Not a big deal, I can do the multiplication in two steps (Matrix3f E=A*B; return E|C ), but maybe there's a better way?

this is because Options is specific to the class Matrix, so you can replace the line:

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Options = Derived1::Options,

by

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Options = Derived1::Flags&RowMajorBit ? RowMajor : 0,

OOOPS !

There's something very bad in what i told you. Basically it only works for fixed-size matrices but not dynamic-size, because a line like

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ColsAtCompileTime = Derived1::ColsAtCompileTime + Derived2::ColsAtCompileTime


would give Dynamic+Dynamic instead of Dynamic !!!

So the solution is rather:

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#define SUM_OR_DYNAMIC(x,y) (x==Dynamic||y==Dynamic)?Dynamic:(x+y)
enum {
 ........
ColsAtCompileTime = SUM_OR_DYNAMIC(Derived1::ColsAtCompileTime, Derived2::ColsAtCompileTime),
         
.........
MaxColsAtCompileTime = SUM_OR_DYNAMIC(Derived1::MaxColsAtCompileTime, Derived2::MaxColsAtCompileTime)
};


Also in the dynamic case I think that you must set the matrix size before you use the comma initializer:

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{
  typename hstack_return::type res(lhs.rows(), lhs.cols()+rhs.cols());
  ...
}


Thanks for such extensive help!

But:

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Options = Derived1::Flags&RowMajorBit ? RowMajor : 0,

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1>z:c++_sharedhelpers_eigen.hpp(28) : error C2440: '=' : cannot convert from 'int' to ''
1>        Conversion to enumeration type requires an explicit cast (static_cast, C-style cast or function-style cast)


That's just that you need to add int(...) somewhere to convert to int (which it will then be able to auto convert to the right enum type). Try around RowMajor for instance.

bjacob wrote:That's just that you need to add int(...) somewhere to convert to int (which it will then be able to auto convert to the right enum type). Try around RowMajor for instance.

Options = Derived1::Flags&RowMajorBit ? (int)RowMajor : 0,
error C2440: '=' : cannot convert from 'int' to ''

Options = Derived1::Flags&RowMajorBit ? int(RowMajor) : 0,
error C2440: '=' : cannot convert from 'int' to ''

Options = Derived1::Flags&RowMajorBit ? static_cast(RowMajor) : 0,
error C2440: '=' : cannot convert from 'int' to ''

Options = Derived1::Flags&RowMajorBit ? RowMajor : RowMajor, // wrong, but...
[!] error C2440: '=' : cannot convert from '' to '' // [!!!]
(So, I guess the problem is second argument, but the error message blows my brain up from '' to '' ??)

Same error:
Options = int(int(Derived1::Flags&RowMajorBit) ? RowMajor : RowMajor),
Options = int(Derived1::Flags&RowMajorBit) ? RowMajor : RowMajor,
Options = int(Derived1::Flags&RowMajorBit ? RowMajor : 0),
error C2440: '=' : cannot convert from 'int' to ''

Oh, dam, I put Options to "typedef" instead of "enum" part. The original line works! Sorry

try this:

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Options = int(Derived1::Flags)&int(RowMajorBit) ? int(RowMajor) : 0,


EDIT: Oh OK glad that it works

Just in case somebody else tries to replicate this function, turns out you need to also res.resize(...) before comma initialization. See here: http://codereview.appspot.com/90077/dif ... :1004/1006 lines 320 (HStack), 328 (VStack)