定義
![克萊羅方程](/img/2/f91/wZwpmLxEjNzQTM5MzN2YjN1UTM1QDN5MjM5ADMwAjMwUzLzczL0QzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
形如 的方程,稱為克萊羅微分方程,這裡 f 是連續可微函式。
![克萊羅方程](/img/9/67d/wZwpmL1UzMyADN2ATN2YjN1UTM1QDN5MjM5ADMwAjMwUzLwUzL3AzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![克萊羅方程](/img/8/c08/wZwpmL1QjN4YDOwQTN2YjN1UTM1QDN5MjM5ADMwAjMwUzL0UzLxEzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
克萊羅方程的通解具有形式:(直線族),此外存在奇解(包絡),其中奇解可以通過方程組:消去參數 p 而得到。
方程求解
方程的通解
![克萊羅方程](/img/3/dcb/wZwpmL0IzN1cTNwUjN2YjN1UTM1QDN5MjM5ADMwAjMwUzL1YzL3IzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
克萊羅方程的通解可以通過令(任意常數),代入原方程中求得。
具體求解步驟
![克萊羅方程](/img/2/f91/wZwpmLxEjNzQTM5MzN2YjN1UTM1QDN5MjM5ADMwAjMwUzLzczL0QzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
已知方程:,
![克萊羅方程](/img/a/16f/wZwpmLxETN5AzMzgzMxYjN1UTM1QDN5MjM5ADMwAjMwUzL4MzL1gzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![克萊羅方程](/img/2/d7e/wZwpmL1IDO0UzM0QjN2YjN1UTM1QDN5MjM5ADMwAjMwUzL0YzLyMzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
對上式左右兩端同時對 x 求導,並令,可得:;
![克萊羅方程](/img/1/44e/wZwpmLzYjN5UDNzEzN2YjN1UTM1QDN5MjM5ADMwAjMwUzLxczLwUzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
即有:。
![克萊羅方程](/img/f/20b/wZwpmL3YTN1gjN1EjN2YjN1UTM1QDN5MjM5ADMwAjMwUzLxYzL2AzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
![克萊羅方程](/img/3/dcb/wZwpmL0IzN1cTNwUjN2YjN1UTM1QDN5MjM5ADMwAjMwUzL1YzL3IzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![克萊羅方程](/img/a/16f/wZwpmLxETN5AzMzgzMxYjN1UTM1QDN5MjM5ADMwAjMwUzL4MzL1gzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![克萊羅方程](/img/8/2b3/wZwpmLyEzN0UDM0gDN2YjN1UTM1QDN5MjM5ADMwAjMwUzL4QzLwUzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
(1)如果,則得到,將其代入到式子中可得:,其中 c 為任意常數,這就是原方程的解。
![克萊羅方程](/img/f/8d4/wZwpmL4QDNwADN4kDN2YjN1UTM1QDN5MjM5ADMwAjMwUzL5QzL3MzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
![克萊羅方程](/img/e/3f1/wZwpmLyMDMxMDN2UzN2YjN1UTM1QDN5MjM5ADMwAjMwUzL1czL2EzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
(2)如果 ,則將該式與原方程聯立,得到方程組: ,消去 p 則得到方程的一個解。求此解的過程與求包絡的過程是一致的。不難驗證,此解正是通解的包絡。由此,克萊羅微分方程的通解為一直線族,即在原方程中以 c 代 p,且此直線族的包絡是方程的奇解。
典例
例1
![克萊羅方程](/img/5/827/wZwpmL4QjMygDNxcDN2YjN1UTM1QDN5MjM5ADMwAjMwUzL3QzLwMzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![克萊羅方程](/img/a/16f/wZwpmLxETN5AzMzgzMxYjN1UTM1QDN5MjM5ADMwAjMwUzL4MzL1gzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
求解方程 ,其中 。
![克萊羅方程](/img/0/0d1/wZwpmL2YDN4YTMwUjN2YjN1UTM1QDN5MjM5ADMwAjMwUzL1YzL0EzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
解:這是克萊羅方程,因而易得其通解為,
![克萊羅方程](/img/f/a69/wZwpmL0cjMyEzM5EjN2YjN1UTM1QDN5MjM5ADMwAjMwUzLxYzLxAzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![克萊羅方程](/img/a/1a5/wZwpmL1gTO1MTNxUzN2YjN1UTM1QDN5MjM5ADMwAjMwUzL1czLyEzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
從方程組 中消去 c,得到奇解:。
方程的通解是直線族,而奇解是通解的包絡。
例2
![克萊羅方程](/img/9/9db/wZwpmL4MTO0ITN2ATN2YjN1UTM1QDN5MjM5ADMwAjMwUzLwUzL4IzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
解方程 。
![克萊羅方程](/img/2/923/wZwpmL4UzNyEDN1YzMxYjN1UTM1QDN5MjM5ADMwAjMwUzL2MzL0AzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![克萊羅方程](/img/b/12e/wZwpmLzITM3MjM3AjN2YjN1UTM1QDN5MjM5ADMwAjMwUzLwYzL0AzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
解:令 ,則有。
![克萊羅方程](/img/f/6a1/wZwpmL2ATMwYzN2EzN2YjN1UTM1QDN5MjM5ADMwAjMwUzLxczLwEzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![克萊羅方程](/img/8/fde/wZwpmL4UTM3QjM2AjMxMzM1UTM1QDN5MjM5ADMwAjMwUzLwIzLxIzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![克萊羅方程](/img/7/2bf/wZwpmLyQTNzEDNzATO2YjN1UTM1QDN5MjM5ADMwAjMwUzLwkzL1gzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![克萊羅方程](/img/1/660/wZwpmLwYTOyEDNzgTN2YjN1UTM1QDN5MjM5ADMwAjMwUzL4UzLzYzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
微分後,以代替,我們得到:或者。
![克萊羅方程](/img/d/c01/wZwpmLyQDOzMjMwQTN2YjN1UTM1QDN5MjM5ADMwAjMwUzL0UzLwUzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
求解這個線性方程後,我們有: 。
![克萊羅方程](/img/f/644/wZwpmL4QTNwQDMzMjN2YjN1UTM1QDN5MjM5ADMwAjMwUzLzYzL3czLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
因此,得到:,
![克萊羅方程](/img/b/12e/wZwpmLzITM3MjM3AjN2YjN1UTM1QDN5MjM5ADMwAjMwUzLwYzL0AzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![克萊羅方程](/img/e/149/wZwpmL2UDN0MjNzgDN2YjN1UTM1QDN5MjM5ADMwAjMwUzL4QzL1czLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
為了求出奇積分,按照一般規則做出方程組: , ,
![克萊羅方程](/img/2/eab/wZwpmL4IzN2MTO3gTN2YjN1UTM1QDN5MjM5ADMwAjMwUzL4UzL0czLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
![克萊羅方程](/img/f/e92/wZwpmL1UzM1AjNygTN2YjN1UTM1QDN5MjM5ADMwAjMwUzL4UzLzAzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
由此得到: ,。
![克萊羅方程](/img/7/a9d/wZwpmLwUDM5IDO5MTN2YjN1UTM1QDN5MjM5ADMwAjMwUzLzUzL3QzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
所以有:。
把 y 代入原方程,可知得到的函式並不是解,因此原方程沒有奇積分。