Matrix class for ruby?

[seepee]

Does anyone know of a functional Matrix math class for ruby that could
multiply, add and substract 3x2 or larger matrices.

The matrix.rb that is in Ruby API cannot multiply anything larger than 2x2
matrices, which makes it useless for 2D or 3D graphics (for instance).

SP

 

[Jakub Hegenbart]

require 'matrix' #or require >rubylibrarypath/matrix.rb

p Matrix[ [25, 93, 33], [0, -1, 66] ] * Matrix[ [1, 53, 33], [1, -21, 77]

ExceptionForMatrix::ErrDimensionMismatch: Matrix dimension mismatch
from /usr/lib/ruby/1.8/matrix.rb:466:in `*' from (irb):4

??

How exactly would you multiply such two matrices?

Jakub

 

[Nicolas Desprès]

Does anyone know of a functional Matrix math class for ruby that could
multiply, add and substract 3x2 or larger matrices.

The matrix.rb that is in Ruby API cannot multiply anything larger than 2x= 2
matrices, which makes it useless for 2D or 3D graphics (for instance).

Are you sure?

$ irb
irb(main):001:0> Matrix[[1,2,3],[1,2,3],[1,2,3]] *
Matrix[[1,2,3],[1,2,3],[1,2,3]]
=3D> Matrix[[6, 12, 18], [6, 12, 18], [6, 12, 18]]
irb(main):002:0> VERSION
=3D> 1.8.4
$

--=20
Nicolas Despr=E8s

 

[Vincent Fourmond]

Does anyone know of a functional Matrix math class for ruby that could
multiply, add and substract 3x2 or larger matrices.

The matrix.rb that is in Ruby API cannot multiply anything larger than 2x2
matrices, which makes it useless for 2D or 3D graphics (for instance).

SP

Problem:
go to terminal, and type "irb" or "irb1.8"

require 'matrix' #or require >rubylibrarypath/matrix.rb
p Matrix[ [25, 93, 33], [0, -1, 66] ] * Matrix[ [1, 53, 33], [1, -21, 77]

Err... Have you done matrix computations for a long time ? You need
that the number of *columns* from the left matrix matches the number of
*lines* from the right matrix. If you try to multiply two 3x2 matrices,
it is rather encouraging that Matrix refuses it...

Try transposing your matrix first, if that is what you need. Are you
dealing with transformation matrices (which are not real matrices) ?

Vincent

 

[Vincent Fourmond]

Does anyone know of a functional Matrix math class for ruby that could
multiply, add and substract 3x2 or larger matrices.

The matrix.rb that is in Ruby API cannot multiply anything larger than 2x2
matrices, which makes it useless for 2D or 3D graphics (for instance).

OK, I understand now: you want graphical transformations. They are
*not* real matrices, but the combination of a real matrix and a
translation vector. So you need special rules to combine them (although
for additions and substractions, standard matrix multiplications should
work). I don't know any package doing that in Ruby -- but if you
consider writing one, that would definitely be an interesting addition.

Cheers !

Vince

 

[Julien Gaugaz]

Does anyone know of a functional Matrix math class for ruby that could
multiply, add and substract 3x2 or larger matrices.

The matrix.rb that is in Ruby API cannot multiply anything larger than 2x2
matrices, which makes it useless for 2D or 3D graphics (for instance).

SP

Problem:
go to terminal, and type "irb" or "irb1.8"

require 'matrix' #or require >rubylibrarypath/matrix.rb
p Matrix[ [25, 93, 33], [0, -1, 66] ] * Matrix[ [1, 53, 33], [1, -21, 77]

ExceptionForMatrix::ErrDimensionMismatch: Matrix dimension mismatch
from /usr/lib/ruby/1.8/matrix.rb:466:in `*' from (irb):4

??

Yes, it's because you cannot multiply a 2x3 matrix with another 2x3
matrix.... try:

Matrix[ [25, 93, 33], [0, -1, 66] ] * Matrix[ [1, 53, 33], [1, -21, 77]].transpose


Julien

 

[Dan Uznanski]

OK, I understand now: you want graphical transformations. They are
*not* real matrices, but the combination of a real matrix and a
translation vector. So you need special rules to combine them (although
for additions and substractions, standard matrix multiplications should
work). I don't know any package doing that in Ruby -- but if you
consider writing one, that would definitely be an interesting addition.

An RST matrix has an implicit 0 0 0 1 row along the bottom. Nothing
more complicated than that.

Actually when dealing with projection matrices, this 'implicit' bottom
row gets used to define the perspective value of the camera.

That said, matrix.rb is very shoddy - it's missing several important
vector operations (like, oh, -Vector and Vector/Numeric), and it uses
Vector*Matrix instead of the correct Matrix*Vector.

Dan

 

[M. Edward (Ed) Borasky]

An RST matrix has an implicit 0 0 0 1 row along the bottom. Nothing
more complicated than that.

Actually when dealing with projection matrices, this 'implicit' bottom
row gets used to define the perspective value of the camera.

That said, matrix.rb is very shoddy - it's missing several important
vector operations (like, oh, -Vector and Vector/Numeric), and it uses
Vector*Matrix instead of the correct Matrix*Vector.

Dan

I wouldn't call it "shoddy". My biggest complaint with Matrix is that a
Matrix is immutable -- if you want to set elements, you have to do so in
an Array and then create a new Matrix from the Array.

The whole rational / complex / matrix / mathn collection looks to me
like an attempt to provide "high-school algebra" constructs in Ruby that
work the way you'd expect them to work. For example, you can get the
*exact* inverse of a non-singular matrix with rational elements, and I
suppose, though I haven't tried it, the same thing for a non-singular
matrix with complex rational elements. For *small* one-off calculations
and calculations where high speed isn't required, they do just that.

However, if what you want to do is, say, lots of graphical
transformations at high speed using floating point arithmetic, like you
might in a video game, you want NArray.

 

[Cameron McBride]

others in this thread have corrected the logical problem.

but let me point out a typical additional response - the included
Matrix library in ruby is NOT FAST. There are other libs that do this
on the C level, such as NArray, that will allow much better
performance for some graphical uses.

Cameron