[julia-users] optimizing a small for loop for simultaneously multiplying and adding two vectors

[Sheehan Olver]

Hi,

Any tips for optimizing the code below?  Here, Q1 and Q2 are 
Vector{Float64} and a and b are Float64.  It seems to be taking an 
unusually long time, and it seems likely there exists a BLAS command that 
will do better, though I couldn't see an appropriate one.

Sheehan




function applygivens!(Q1,Qk,a,b)
    for j=1:length(Q1)
        @inbounds Q1[j],Qk[j]=a*Q1[j]+b*Qk[j],-b*Q1[j]+a*Qk[j]
    end
end