Re: [Toon-members] stacking two matrices with slices.

[E. Rosten]

On Wed, 8 Jul 2009, Damian Eads wrote:

> Hi,

There were a number of bugs (now fixes). In addition:


> I would like to stack two matrices, -1*identity and the identity
> matrix using TooN slices. I've tried to do this with the following
> code:
>
>  template <int Size, typename PixelType=float>
>  struct MatrixPrimitives {
>    static Matrix <Size*2, Size, PixelType> negI_I(int size=Size) {
>      Matrix <Size*2, Size, PixelType> X;
>      X.slice<0,     0,     Size, Size>() = -1.0 * Identity;  // error
>      X.slice<Size,  0,     Size, Size>() = Identity;         // error
>      return X;
>    }
>  };


This is a C++-ism. Because the type X is not fully determined when the 
struct is written, it doesn't know that slice is a template. So, you have 
to be explicit:

   X.template slice<0, 0, Size, Size>() = ...


>  template <typename PixelType>
>  struct MatrixPrimitives<-1, PixelType> {
>    static Matrix <Dynamic, Dynamic, PixelType> negI_I(int size) {
>      Matrix <Dynamic, Dynamic, PixelType> X(2*size, size);
>      X.slice<>(0,     0,     size, size) = -1.0 * Identity(size); // error
>      X.slice<>(size,  0,     size, size) = Identity(size);   // error
>      return X;
>    }
>  };
>
> but I get a compiler error before instantiating MatrixPrimitives,

That was a documentation bug (now fixed). Dynamic slices don't take 
template arguments:

      X.slice(size,  0,     size, size) = Identity(size);   // error

> To gain some insights, in a separate program (prog3.cpp), I tried
> instantiating Matrix with resolved constants (e.g. 6 and 3) for the
> template arguments then did slicing,
>
> #include <TooN/TooN.h>
>
> using namespace TooN;
>
> int main() {
>  Matrix <6, 3, float> Xf;
>  Xf.slice<0, 0, 3, 3>() = Identity(3);
>  Matrix <6, 3, double> Xd;
>  Xd.slice<0, 0, 3, 3>() = Identity(3);
>  Matrix <6, 3, int> Xi;
>  Xi.slice<0, 0, 3, 3>() = Identity(3);
> }
>
> and the program compiles with a benign precision warning,
>
> bash-3.2$ g++ prog1.cpp -I/usr/local/include -c -o prog1.o
> /usr/local/include/TooN/internal/objects.h: In member function ?void
> TooN::Operator<TooN::Internal::ScaledIdentity<Pr>
> > ::eval(TooN::Matrix<Rows2, Cols2, Precision2, Base2>&) const [with
> int R = 3, int C = 3, P = int, B = TooN::Internal::Slice<3, 1>, Pr =
> double]?:
> /usr/local/include/TooN/internal/matrix.hh:111:   instantiated from
> ?TooN::Matrix<Rows, Cols, Precision, Base>& TooN::Matrix<Rows, Cols,
> Precision, Base>::operator=(const TooN::Operator<Op>&) [with Op =
> TooN::Internal::SizedIdentity<double>, int Rows = 3, int Cols = 3,
> Precision = int, Layout = TooN::Internal::Slice<3, 1>]?
> prog1.cpp:11:   instantiated from here
> /usr/local/include/TooN/internal/objects.h:195: warning: converting to
> ?int? from ?const double?
> bash-3.2$

This is another bug (now fixed). Idendity used to hold a double and then 
assign it where required. This causes a warning when assigning it to an 
int. This has now been replaced with a generic One type which can be 
assigned efficiently to anything with no warnings.

By the way, in the static sized case, you don't need to provide a size to 
Identity, eg:

Xd.slice<0, 0, 3, 3>() = Identity;

In fact, if you do provide a size (even an incorrect one) it will be 
silently ignored.


> It looks like the compiler wants the template arguments to be resolved
> before instantiation. How do I get around this?
>
> Also unexpected, if I use non-constant *function* (not template!)
> arguments when calling slice, I get a compiler error.

Same doc bug as before. If you remove the empty template brackes <> for 
slice, then it will compile.

> Thanks in advance,

Thanks for the bug report!

-Ed

--
(You can't go wrong with psycho-rats.)(http://mi.eng.cam.ac.uk/~er258)

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