Could anyone make this run faster?

[DNF]

@Ahmed_Salih

function Optim∇ᵢWᵢⱼ(αD,q,xᵢⱼ,h)
    # Skip distances outside the support of the kernel:
    if q < 0.0 || q > 2.0
        return SVector(0.0,0.0,0.0)
    end

    Fac    = αD * 1/h * (5*(q-2)^3*q)/8 * (1/(q*h+1e-6))

    gradWx = Fac * xᵢⱼ[1]
    gradWy = Fac * xᵢⱼ[2]
    gradWz = Fac * xᵢⱼ[3]

    return SVector(gradWx,gradWy,gradWz)
end

Probably not faster, but more elegant and general:

function Optim∇ᵢWᵢⱼ(αD,q,xᵢⱼ,h)
    # Skip distances outside the support of the kernel:
    if 0 <= q <= 2
        Fac = αD*5*(q-2)^3*q / (8h*(q*h+1e-6)) 
    else
        Fac = 0.0 # or return zero(xᵢⱼ) 
    end
    return Fac .* xᵢⱼ
end