基本介紹
傅汝蘭尼積分是一種特殊的含參變數的廣義積分,形如
![傅汝蘭尼積分](/img/d/201/wZwpmL1QDOzYDM3EzNxMzM1UTM1QDN5MjM5ADMwAjMwUzLxczLygzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
的廣義積分,其中f在(0,+∞)上連續。可精確計算的情形有 :
![傅汝蘭尼積分](/img/5/134/wZwpmLxUTM4kDN1kDOxMzM1UTM1QDN5MjM5ADMwAjMwUzL5gzLxMzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
1.當f(0+)∈R, f(x)=f(+∞)∈R時,積分值為(f(0+)-f(+∞))ln(b/a)。
2.當f(0+)∈R,且存在A≥0,使
![傅汝蘭尼積分](/img/f/5cf/wZwpmLzITNxcDNxEDOxMzM1UTM1QDN5MjM5ADMwAjMwUzLxgzLxQzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
收斂時,積分值為f(0+)ln(b/a);
3.當f(+∞)∈R,且存在A>0,使
![傅汝蘭尼積分](/img/1/ad1/wZwpmL0gzN1MzN3AzNwMzM1UTM1QDN5MjM5ADMwAjMwUzLwczL3gzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
收斂時,積分值為f(+∞)ln(b/a) 。
傅汝蘭尼積分的證明
![傅汝蘭尼積分](/img/6/aba/wZwpmLxQjMxEDN0cjNxMzM1UTM1QDN5MjM5ADMwAjMwUzL3YzLxAzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
![傅汝蘭尼積分](/img/2/c7d/wZwpmL4EDO4gzN0gzNxMzM1UTM1QDN5MjM5ADMwAjMwUzL4czLyYzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
![傅汝蘭尼積分](/img/d/420/wZwpmLycDM0ETNyQTNxMzM1UTM1QDN5MjM5ADMwAjMwUzL0UzLzQzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
定理1 設 是定義在閉區間 的(二變數的)連續函式,讓 ,此時,下列性質成立 。
![傅汝蘭尼積分](/img/5/f0c/wZwpmL0AjN5ITNzUTMxMzM1UTM1QDN5MjM5ADMwAjMwUzL1EzL1MzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
(i)F在 上連續。
![傅汝蘭尼積分](/img/0/81a/wZwpmLwcjNzczMzAjNwMzM1UTM1QDN5MjM5ADMwAjMwUzLwYzLxYzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
(ii)
![傅汝蘭尼積分](/img/b/229/wZwpmL0cTO2YzN0cTOwMzM1UTM1QDN5MjM5ADMwAjMwUzL3kzL0MzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
(iii)偏導函式 如在D連續,則F在[a,b]可微分而且
![傅汝蘭尼積分](/img/6/f88/wZwpmL1EDN3EDMwYDOwMzM1UTM1QDN5MjM5ADMwAjMwUzL2gzL2UzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
(以上定理的證明請參考相應文獻)
![傅汝蘭尼積分](/img/9/459/wZwpmL4QzMwETN4gjNwMzM1UTM1QDN5MjM5ADMwAjMwUzL4YzL0IzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![傅汝蘭尼積分](/img/6/0ee/wZwpmL1ADOwIDO1ITOwMzM1UTM1QDN5MjM5ADMwAjMwUzLykzLwgzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
Frullani的積分 f是 上的連續函式,若對任意的 存在,則
![傅汝蘭尼積分](/img/3/04f/wZwpmLxcDM1ITN2kTNxMzM1UTM1QDN5MjM5ADMwAjMwUzL5UzL3gzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
稱此為Frullani的積分 。
證明對任意α
![傅汝蘭尼積分](/img/e/13e/wZwpmLwADN3EDMwADOwMzM1UTM1QDN5MjM5ADMwAjMwUzLwgzLxAzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
![傅汝蘭尼積分](/img/0/7cd/wZwpmLwEDN5kjN1UzMxMzM1UTM1QDN5MjM5ADMwAjMwUzL1MzL0EzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
同理
![傅汝蘭尼積分](/img/e/d07/wZwpmLyYTNzITOxMzNxMzM1UTM1QDN5MjM5ADMwAjMwUzLzczL2MzLt92YucmbvRWdo5Cd0FmLxE2LvoDc0RHa.jpg)
所以
![傅汝蘭尼積分](/img/c/054/wZwpmLyIDO3gDOyQDOwMzM1UTM1QDN5MjM5ADMwAjMwUzL0gzL1UzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
![傅汝蘭尼積分](/img/0/e97/wZwpmLzEzM3ETO2YzNwMzM1UTM1QDN5MjM5ADMwAjMwUzL2czL1gzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
現令 ,在D的各點(x,α)研究與它對應的實數值f(αx)/x的函式,這個函式在閉區間D是連續的。因此,根據以上定理的(i),由
![傅汝蘭尼積分](/img/f/dcc/wZwpmL0QzMycDO2YzNwMzM1UTM1QDN5MjM5ADMwAjMwUzL2czLzEzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)
所定義的函式F在[0,1)連續。故
![傅汝蘭尼積分](/img/6/bf9/wZwpmL3gDO0ADN1cjNxMzM1UTM1QDN5MjM5ADMwAjMwUzL3YzL4YzLt92YucmbvRWdo5Cd0FmLzE2LvoDc0RHa.jpg)
即
![傅汝蘭尼積分](/img/e/62e/wZwpmL3IDMxYzM3gjNwMzM1UTM1QDN5MjM5ADMwAjMwUzL4YzLwIzLt92YucmbvRWdo5Cd0FmL0E2LvoDc0RHa.jpg)
![傅汝蘭尼積分](/img/1/402/wZwpmL0gDO3MjM2gzNwMzM1UTM1QDN5MjM5ADMwAjMwUzL4czL0gzLt92YucmbvRWdo5Cd0FmLyE2LvoDc0RHa.jpg)
這樣, 時,(1)的左邊收斂,且
![傅汝蘭尼積分](/img/a/e90/wZwpmL1YzM2ITN1IzNwMzM1UTM1QDN5MjM5ADMwAjMwUzLyczLzMzLt92YucmbvRWdo5Cd0FmLwE2LvoDc0RHa.jpg)