[ITK-users] VariableLengthVector and multiplication

[Cyril Mory]

Dear ITK users,

I am using itk::VectorImage in some of my code, which uses 
itk::VariableLengthVector as pixel type. And I am wondering why 
itk::VariableLengthVector has so little support for multiplication. 
Currently, the * operator only supports multiplication by a scalar.

It probably isn't simple, but I would need three additional kinds of 
multiplication:

- dot product with another VariableLengthVector (that has the same 
length, although it is probably a waste of time to perform the check 
every time), returning a scalar

- component-wise multiplication, returning a VariableLengthVector of the 
same length

- left or right multiplication with a matrix (possibly an 
itk::VariableSizeMatrix) that has the correct size, but I understand 
that this is probably the most complex one, and since it only occurs 
rarely in my code, I can handle it with conversions to vnl::vector and 
vnl::matrix

Are there constraints that prevent at least the dot product and 
component-wise multiplication operators from being implemented ? If not, 
then I'd be happy to give it a try. Since both differ only by the return 
type, two different operators would have to be used (I guess). Do you 
have suggestions (which one should use *, and what should be the other 
operator) ? In itk::Vector and itk::CovariantVector, the * operator is 
used for dot product.

Regards,

Cyril