Simple question on rbgsl vectors

Ruby
#1

Hi,

I’m trying to do a simple thing : access elements of a vector
specified by their index. In Matlab/Octave i would do,

newVector=oldVector( [1, 3, 56, 72] )

How does this work with Ruby vectors?

oldVector.get(3,4,5) returns the first 3 elements, where I would
expect the 2nd, 3d and 4th.

I’ve had to do a twisted version of this using arrays and lists,

a2=[]
(0…200).step(10) {|i| a2 << a[i] }

I find it very inefficient and annoying, plus I do need to use
vectors rather than arrays and lists and do not really know how to
convert between these three :frowning:

Oh, and just a quick question: how can i do two instructions in one
block ? I have to repeat the same instructions over and over like
shown below…

a2=[]
b2=[]
(0…200).step(10) {|i| a2 << a[i] }
(0…200).step(10) {|i| b2 << b[i] }

Best regards,

baptiste

#2

Dear Baptiste,

you can get reference for the gsl bindings for ruby
here:

http://rb-gsl.rubyforge.org/ref.html .

oldVector.get(3,4,5) returns the first 3 elements, where I would
expect the 2nd, 3d and 4th.

oldVector.get([3,4,5]) worked for me - I’m not quite sure
why this:

oldVector.get(3,4,5) returns the first 3 elements

happens…

I’ve had to do a twisted version of this using arrays and lists,

a2=[]
(0…200).step(10) {|i| a2 << a[i] }

I find it very inefficient and annoying, plus I do need to use
vectors rather than arrays and lists and do not really know how to
convert between these three :frowning:

You’ll find info about that on the website given above.

Oh, and just a quick question: how can i do two instructions in one
block ? I have to repeat the same instructions over and over like
shown below…

You can use the same index several times:

(0…200).step(10) {|i| a2 << a[i] ; b2<<b[i] }

Best regards,

Axel

#3

Thanks for the reply, although I’m very confused now.

Does anybody see this odd behavior:

irb(main):001:0> require(“rbgsl”)
=> true
irb(main):002:0> v = GSL::Vector[0…5]
=> GSL::Vector: [ 0.000e+00 1.000e+00 2.000e+00 3.000e+00 4.000e+00
5.000e+00 ]
irb(main):003:0> v[2]
=> 2.0
irb(main):004:0> v[1, 3, 4]
=> GSL::Vector: [ 0.000e+00 1.000e+00 2.000e+00 ]

**** where is should expect ****

=> GSL::Vector: [ 1.000e+00 3.000e+00 4.000e+00 ]

This is most annoying as I cannot do anything useful with such behavior.

irb 0.9.5 (05/04/13)
ruby 1.8.6 (2007-03-13 patch level 0) [i386 linux]

Thanks,

baptiste