Jacobi行列式是以$n$个$n$元函数
$$y_i=y_i(x_1,x_2,\cdots,x_n)，i=1,2,\cdots,n$$
　　的偏导数为元素的行列式
$$ \left| {\begin{array}{*{20}{c}} \frac{\partial y_1}{\partial x_1}&\cdots&\frac{\partial y_1}{\partial x_n}\\ \vdots&\ddots&\vdots\\ \frac{\partial y_n}{\partial x_1}&\cdots&\frac{\partial y_n}{\partial x_n} \end{array}} \right|$$
　　常记为
$$\frac{\partial (y_1,y_2,\cdots,y_n)}{\partial (x_1,x_2,\cdots,x_n)}$$