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Andrey Akinshin added subsection_General_complex_Prony_N__.tex
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\subsection{General complex Prony, $N$D}
Let's consider the following system:
$$
m_k = \sum_{j=1}^N a_j x_j^k, \quad k \in \{0, 1, \ldots, 2N-1\}.
$$
Introduce variables $\{u_j\}$:
$$
\begin{cases}
u_1 = x_1 + x_2 + \ldots + x_N, \\
u_2 = x_1x_2 + x_1x_3 + \ldots + x_{N-1}x_N, \\
\ldots \\
u_N = x_1x_2\ldots x_N.
\end{cases}
$$
From the Viet's theorem, we have:
\begin{equation}
\label{eq3}
m_{l} = m_{l-1}u_1 - m_{l-2}u_2 + \ldots + (-1)^{N-1}m_{l-N} u_N.
\end{equation}
Thus, $\{u_j\}$ are solution of the following system of equations:
$$
\begin{pmatrix}
m_{N-1} & -m_{N-2} & \ldots & (-1)^{N-1} m_0 \\
m_{N} & -m_{N-1} & \ldots & (-1)^{N-1} m_1 \\
\vdots & \vdots & \ddots & \vdots \\
m_{2N-2} & -m_{2N-3} & \ldots & (-1)^{N-1} m_{N-1}
\end{pmatrix}
\times
\begin{pmatrix}
u_1 \\ u_2 \\ \vdots \\ u_N
\end{pmatrix}
=
\begin{pmatrix}
m_N \\ m_{N+1} \\ \vdots \\ m_{2N-1} \\
\end{pmatrix}.
$$
We can find $\{x_j\}$ from the following equation:
$$
x^N - u_1 x^{N-1} + \ldots + (-1)^N u_N = 0.
$$
We can find $\{a_j\}$ as a solution of the following system:
$$
\begin{pmatrix}
1 & 1 & \ldots & 1 \\
x_1 & x_2 & \ldots & x_d \\
x_1^2 & x_2^2 & \ldots & x_N^2 \\
\vdots & \vdots & \ddots & \vdots \\
x_1^{N-1} & x_2^{N-1} & \ldots & x_N^{N-1} \\
\end{pmatrix}
\times
\begin{pmatrix}
a_1 \\ a_2 \\ a_3\\ \vdots \\ a_N
\end{pmatrix}
=
\begin{pmatrix}
m_0 \\ m_1 \\ m_2 \\ \vdots \\ m_{N-1}
\end{pmatrix}.
$$