我有以下等式:
eq1 := 2*diff(phi(r),r)/r+diff(phi(r),$(r,2)) + psi(r)^2*phi(r);
我想将自变量r更改为1 / z,即变量r = 1 / z的变化。如何使用新变量
编写此等式答案 0 :(得分:0)
eq1 := 2*diff(phi(r),r)/r+diff(phi(r),$(r,2)) + psi(r)^2*phi(r);
/ d \
2 |--- phi(r)| / 2 \
\ dr / | d | 2
eq1 := -------------- + |---- phi(r)| + psi(r) phi(r)
r | 2 |
\ dr /
PDEtools[dchange](r=1/z, eq1);
/ / 2 \\
3 / d \ 2 | / d \ 2 | d || 2
-2 z |--- phi(z)| - z |-2 z |--- phi(z)| - z |---- phi(z)|| + psi(z) phi(z)
\ dz / | \ dz / | 2 ||
\ \ dz //
simplify(%);
/ 2 \
| d | 4 2
|---- phi(z)| z + psi(z) phi(z)
| 2 |
\ dz /