latex效果测试

[latexpage]
At first, we sample $f(x)$ in the $N$ ($N$ is odd) equidistant points around $x^*$:
[
f_k = f(x_k),: x_k = x^*+kh,: k=-frac{N-1}{2},dots,frac{N-1}{2}
]
where $h$ is some step.
Then we interpolate points ${(x_k,f_k)}$ by polynomial
begin{equation} label{eq:poly}
P_{N-1}(x)=sum_{j=0}^{N-1}{a_jx^j}
end{equation}
Its coefficients ${a_j}$ are found as a solution of system of linear equations:
begin{equation} label{eq:sys}
left{ P_{N-1}(x_k) = f_kright},quad k=-frac{N-1}{2},dots,frac{N-1}{2}
end{equation}
Here are references to existing equations: (ref{eq:poly}), (ref{eq:sys}).
Here is reference to non-existing equation (ref{eq:unknown}).

begin{tikzpicture}
[+preamble]
    usepackage{tikz}
    usepackage{pgfplots}
    pgfplotsset{compat=newest}
[/preamble]
    begin{axis}
       addplot3[surf,domain=0:360,samples=40] {cos(x)*cos(y)};
    end{axis}
end{tikzpicture}