Crank-Nicolson 格式 <img src="https://latex.codecogs.com/png.image?\dpi{110}\frac{T_{i}^{n+1}-T_{i}^{n}}{\Delta+t}&space;=&space;\frac{1}{2}\left(D\frac{T^n_{i+1}-2T^n_{i}+T^n_{i-1}}{\Delta+x^2}+D\frac{T^{n+1}_{i+1}-2T^{n+1}_{i}+T^{n+1}_{i-1}}{\Delta+x^2}\right)" title="https://latex.codecogs.com/png.image?\dpi{110}\frac{T_{i}^{n+1}-T_{i}^{n}}{\Delta+t} = \frac{1}{2}\left(D\frac{T^n_{i+1}-2T^n_{i}+T^n_{i-1}}{\Delta+x^2}+D\frac{T^{n+1}_{i+1}-2T^{n+1}_{i}+T^{n+1}_{i-1}}{\Delta+x^2}\right)" />