Re: Successive Over-Relaxation ... what is wrong? Improvements?

[marco atzeri]

On 11/6/2012 4:54 PM, Joza wrote:
> Thanks for the info...stuff to think about! Besides all this, is there any
> neat ways to speed out plain old FOR loops using vectors? For example, the
> ones I have below:
>
> for i=1:n
>                 sum = 0.0;
>                 
>                 if i==1
>                         for j=1:2
>                                 sum = sum + A(i,j)*x(j);
>                         end
>                 elseif i==n
>                         for j=n-1:n
>                                 sum = sum + A(i,j)*x(j);
>                         end
>                 else
>                         for j=i-1:i+1
>                                 sum = sum + A(i,j)*x(j);
>                         end
>                 end

what about multiplication of sparse matrix and vector ?

assuming A sparse (n*n) with just 2 or 3 not-zero elements per
row and x vector (n*1)

my_sum=sum(A*x)

Regards
Marco