Re: Using ruby for scientific computing

Le 8 sept. 2012 =C3=A0 19:39, Panagiotis Atmatzidis <[e-mail]> =
a =C3=A9crit :

> Hello,
>=20
> On 8 =CE=A3=CE=B5=CF=80 2012, at 18:06 , Olivier Saut =
<[e-mail]> wrote:
>=20
>> Hi all,
>>=20
>> For pedagogic purposes, I am trying to solve simple partial =
differential
>> equations (say a diffusion equation on a regular mesh in 2D) with =
Ruby.
>> Using the NArray gem, I have built a satisfactory tool from an =
interface
>> (and ease of use) point of view but the performance are suboptimal.=20=

>=20
> Is the code available on a public repo?

Not yet, but I plan to share it as soon as I am convinced it is usable =
for my students.=20

>=20
>> I am now wondering what is the right way to improve my code
>> performance-wise. I am doing a lot of matrix-vector and vector-vector
>> products.=20
>>=20
>> =46rom 2 2D NArrays describing two scalar fields, dot-product is =
implemented as :
>>=20
>> def dot_product(vec_a, vec_b)=20
>>       dot_product=3D(vec_a*vec_b">vec_a*vec_b).sum=20
>> end

The definition above is wrong, the right ones

def dot_product(vec_a, vec_b)
	(vec_a*vec_b).sum
end


>>=20
>> and as I am working with sparse matrices, (for the time being) a =
matrix
>> is an Array of Hashes. Each key of the hash contains the index of the
>> non-vanishing coefficients (the value of this coefficient is the =
value
>> of the Hash) of the matrix. For the identity matrix it gives
>>=20
>> def identity(sizeX, sizeY)
>>       mat=3D[]
>>       (0..sizeX*sizeY">sizeX*sizeY).each { |ind|
>>           mat << {ind=3D>1.0}
>>       }
>>       mat
>> end
>>=20
>>=20
>> Matrix vector product is then defined as
>>=20
>> def matrix_vector_product(mat, vector)=20
>>       ff=3DNArray.float(100,100)
>>       (0..100*100).each { |ind|
>>           matrix[ind].each do |key,value|
>>               ff[[ind]]+=3Dvalue*vector[[key]][0]
>>           end
>>       }
>>       ff
>> end
>>=20
>> I am wondering what is the best way to tackle this performance =
problem :
>> 1. Improve the ruby code (and how? :) Should I avoid using hashes?
>> 2. Write an extension to perform these operations in C. BTW is there =
a
>> way to access directly NArray data (without copy) from a C extension?
>> 3. Use a wrapper like Ruby-lapack
>> (
>> https://rubyforge.org/projects/ruby-lapack/
>> ).
>>=20
>> What do you think?=20
>>=20
>> Thanks for your help !



Best regards,
						       	                	=
- Olivier