Numerical_analysis Here I am collecting my documentation on numerical analysis PDE TYPES \begin{equation} \alpha=2c \end{equation} $$ a(x_{1},x_{2}){\frac {\partial ^{2}u}{\partial x_{1}^{2}}}+b(x_{1},x_{2}){\frac {\partial ^{2}u}{\partial x_{1}\partial x_{2}}}+c(x_{1},x_{2}){\frac {\partial ^{2}u}{\partial x_{2}^{2}}}+d(x_{1},x_{2}){\frac {\partial u}{\partial x_{1}}}+e(x_{1},x_{2}){\frac {\partial u}{\partial x_{2}}}+f(x_{1},x_{2})u=g(x_{1},x_{2}) $$