[Insight-users] Question about workings of ExponentialDeformationFieldImageFilter

[Anja Ende]

> This addition is need to compute the composition. Let u, v and w be
> displacement fields, we want w such that
>  Id+w = (Id + u) o (Id + v)
>          = Id + v + u_warped_by_v
>
> meaning
>  w = v + u_warped_by_v

Thanks for this Tom. How is this coming about though?

By distributive law, we have:

(Id+u)o(Id+v) = (Id+u)o(Id) + (Id+u)o(v)

I am guessing the second bit generates the u_warped_by_v bit. How does
(Id+u)o(Id) results in Id.

Thanks,

Anja