可導性與連續性
如果 f是在 x處可導的函式,則 f一定在 x處連續,特別地,任何可導函式一定在其定義域內每一點都連續。反過來並不一定。事實上,存在一個在其定義域上處處連續函式,但處處不可導。
魏爾斯特拉斯函式
魏爾斯特拉斯函式 是由魏爾斯特拉斯構造出的一個函式,其在R上處處連續,但處處不可導。
![可導函式](/img/2/dd7/wZwpmLwIzN5UTOxkTN0YzM1UTM1QDN5MjM5ADMwAjMwUzL5UzLzMzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![可導函式](/img/7/9ca/wZwpmL3QTN5IzNwgTN2IDN0UTMyITNykTO0EDMwAjMwUzL4UzLyIzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![可導函式](/img/9/b7b/wZwpmLxUTM4kDNykzN5ADN0UTMyITNykTO0EDMwAjMwUzL5czL0YzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![可導函式](/img/d/07d/wZwpmL3IDOxkDNzMTMzEDN0UTMyITNykTO0EDMwAjMwUzLzEzL1MzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
其中 , 是正奇數,且 滿足
![可導函式](/img/0/bec/wZwpmLwEjMxITM0gzNxMzM1UTM1QDN5MjM5ADMwAjMwUzL4czLxIzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
可導函式類
![可導函式](/img/8/778/wZwpmL2MzN5UzM2MzNwIDN0UTMyITNykTO0EDMwAjMwUzLzczL4MzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![可導函式](/img/9/dec/wZwpmLyIzM0ADMwMTOwMzM1UTM1QDN5MjM5ADMwAjMwUzLzkzLxEzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![可導函式](/img/8/778/wZwpmL2MzN5UzM2MzNwIDN0UTMyITNykTO0EDMwAjMwUzLzczL4MzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![可導函式](/img/2/743/wZwpmLyYDNwczNzQzN2UzM1UTM1QDN5MjM5ADMwAjMwUzL0czLwEzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
![可導函式](/img/9/dec/wZwpmLyIzM0ADMwMTOwMzM1UTM1QDN5MjM5ADMwAjMwUzLzkzLxEzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![可導函式](/img/8/778/wZwpmL2MzN5UzM2MzNwIDN0UTMyITNykTO0EDMwAjMwUzLzczL4MzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![可導函式](/img/a/c66/wZwpmL1cDNxQjN3QDOxMzM1UTM1QDN5MjM5ADMwAjMwUzL0gzLxAzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
![可導函式](/img/8/778/wZwpmL2MzN5UzM2MzNwIDN0UTMyITNykTO0EDMwAjMwUzLzczL4MzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![可導函式](/img/8/778/wZwpmL2MzN5UzM2MzNwIDN0UTMyITNykTO0EDMwAjMwUzLzczL4MzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![可導函式](/img/c/185/wZwpmL0YDM3kDO2gTN2UzM1UTM1QDN5MjM5ADMwAjMwUzL4UzL3AzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
稱 是 連續的,如果其導函式存在且是連續的。稱 是 連續的,如果其導數是 的。一般地,稱 是 連續的,如果其1階,直到k階導數存在且是連續的。若 任意階導數存在,則稱 是光滑的,或 的。
![可導函式](/img/a/c66/wZwpmL1cDNxQjN3QDOxMzM1UTM1QDN5MjM5ADMwAjMwUzL0gzLxAzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
全體 函數類構成Banach空間。
高維可導性
![可導函式](/img/c/ee1/wZwpmL4YTN1ADM4MTN0YzM1UTM1QDN5MjM5ADMwAjMwUzLzUzLyMzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![可導函式](/img/d/58f/wZwpmLyEjN4ITNyMTMzEDN0UTMyITNykTO0EDMwAjMwUzLzEzLxczLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![可導函式](/img/d/adc/wZwpmLyIDNxgTM4QzN0YzM1UTM1QDN5MjM5ADMwAjMwUzL0czL0MzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
稱 在 處可導,如果存在一線性映射 滿足
![可導函式](/img/2/2e1/wZwpmLwgzM3ITMwUzN2UzM1UTM1QDN5MjM5ADMwAjMwUzL1czL1gzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![可導函式](/img/8/778/wZwpmL2MzN5UzM2MzNwIDN0UTMyITNykTO0EDMwAjMwUzLzczL4MzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![可導函式](/img/8/778/wZwpmL2MzN5UzM2MzNwIDN0UTMyITNykTO0EDMwAjMwUzLzczL4MzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
如果 在定義域上任意點可導,則稱為可導函式。
注意:高維函式的偏導數存在,不一定可導。
例子
![可導函式](/img/0/539/wZwpmLxATOwgDM4IjN0YzM1UTM1QDN5MjM5ADMwAjMwUzLyYzL1QzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
在(0,0)處不可導,但是偏導數存在。
複函數的可導性
![可導函式](/img/9/825/wZwpmLwgTMxEDOwMjN0YzM1UTM1QDN5MjM5ADMwAjMwUzLzYzL2gzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
![可導函式](/img/1/bcb/wZwpmLwYjN0kjNwgjN2UzM1UTM1QDN5MjM5ADMwAjMwUzL4YzL1IzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
在複分析中,稱函式是可導的,如果函式在定義域中每一點處是全純的。複函數可導等價於Cauchy–Riemann方程 。即,若可導當僅當滿足下列方程:
![可導函式](/img/e/c07/wZwpmL3gTO3gzMwETN0YzM1UTM1QDN5MjM5ADMwAjMwUzLxUzL0MzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
或等價地寫成
![可導函式](/img/1/2b1/wZwpmLyUzN4MDM1gjN0YzM1UTM1QDN5MjM5ADMwAjMwUzL4YzL0AzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
流形上函式的可導性
![可導函式](/img/8/778/wZwpmL2MzN5UzM2MzNwIDN0UTMyITNykTO0EDMwAjMwUzLzczL4MzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![可導函式](/img/8/778/wZwpmL2MzN5UzM2MzNwIDN0UTMyITNykTO0EDMwAjMwUzLzczL4MzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
流形上的函式稱為可導的,如果在任意的局部坐標系下,的局部表示是可導函式。