Let $\vec{U}=\{u_0,u_1,\ldots,u_m\}$ denotes a non-decreasing sequence of real numbers, i.e, $u_i\leq u_{i+1} \quad i=0,1,2\ldots m-1$.

and the $i$-th B-spline basis function of $p$-degree, denoted by $N_{i,p}(u)$, is defined as below:

$$N_{i,0}(u)=
\begin{cases}
   1 & u_i\leq u<u_{i+1}\\
   0 & otherwise
   \end{cases}
$$
$$N_{i,p}(u)=\frac{u-u_i}{u_{i+p}-u_i}N_{i,p-1}(u)+\frac{u_{i+p+1}-u}{u_{i+p+1}-u_{i+1}}N_{i+1,p-1}(u)
$$

By reading the textbook The *NURBS* Book, I can know the following recursive formula about the derivetive of $N_{i,p}(u)$. Namely,

$$
\frac{d}{du}N_{i,p}(u)=p\left[ \frac{N_{i,p-1}(u)}{u_{i+p}-u_i}-\frac{N_{i+1,p-1}(u)}{u_{i+p+1}-u_{i+1}} \right]
$$

In addition, I can also understand the *verification process* by mathematical induction that the author given in the textbook. However, I would like to know **where this formula came from**. Namely, 

- How to **deduce** the derivative formmula of the B-spline basis function $N_{i,p}(u)$?

- Although the author has given the reference [The Computation of all the Derivatives of a B-spline Basis](http://imamat.oxfordjournals.org/content/17/1/15.short) in the Bibiology, I cannot download that paper by the libriary of our university.