在MATLAB中，如何用diff命令求函数的高阶导数
用diff命令还可以求函数的高阶导数，其使用格式为：
diff(f,n)
例题 求函数的高阶导数
>> f=exp(-2*x)*cos(3*x^(1/2))
f =
cos(3*x^(1/2))/exp(2*x)
>> diff(f,3)
ans =
(27*cos(3*x^(1/2)))/(2*x*exp(2*x))- (8*cos(3*x^(1/2)))/exp(2*x)+
(27*cos(3*x^(1/2)))/(8*x^2*exp(2*x))-
(18*sin(3*x^(1/2)))/(x^(1/2)*exp(2*x))
(9*sin(3*x^(1/2)))/(8*x^(3/2)*exp(2*x))
(9*sin(3*x^(1/2)))/(8*x^(5/2)*exp(2*x))
>> pretty(ans)
27 #2 8 #2 27 #2
------------ - -------- + -------------
2 x exp(2 x) exp(2 x) 28 x exp(2 x)
18 #1 9 #1 9 #1
------------- - --------------- - --------------
1/2 3/2 5/2
x exp(2 x) 8 x exp(2 x) 8 x exp(2 x)
where
1/2
#1 = sin(3 x )
1/2
#2 = cos(3 x )
