\[a_{m}(\mathbf{y})=\sum_{n=1}^{K+1}\frac{P_{mn}(\mathbf{y})G_{n}(\mathbf{y})}{(%
t_{n}(\mathbf{x}(\mathbf{y})))^{m+1}\prod\limits_{\begin{subarray}{c}l=1\\
l\neq n\end{subarray}}^{K+1}(t_{n}(\mathbf{x}(\mathbf{y}))-t_{l}(\mathbf{x}(%
\mathbf{y})))},\]