function dot_prod(a,b)
    na = length(a)
    nb = length(b)
    #assert does if and in the case that the condition is wrong returns an error which stops the function
    @assert na == nb "Lengths of vectors must match."

    s = 0,0
    @inbounds for i in eachindex(a)
        s = s + a[i]*b[i]
    end
end