您如何在函数句柄上进行符号区分? [英] how do you do symbolic differentiation on function handle?

问题描述

请问我是否定义以下内容:

Say if i define the following:

g = @(x) x/sqrt(x^2+1)

我如何获得g的导数函数，然后可以用它在不同的点求值?

How do i get the derivative function for g, which i can then use to evaluate at different points?

我尝试了符号数学工具包，并尝试了以下方法:

I tried the symbolic math toolkit, and tried the following:

>> syms x

>> f = x/sqrt(x^2+1)

f =

x/(x^2 + 1)^(1/2)

>> diff(f)

ans =

1/(x^2 + 1)^(1/2) - x^2/(x^2 + 1)^(3/2)

但是，我无法弄清楚如何将其转换为函数句柄/在不同点进行求值.但是，我更喜欢在function_handle上进行区分.

However, i cannot figure out how to turn this into a function handle/evaluate at different points. However, i prefer doing differentiation on function_handle.

非常感谢！

Jason

推荐答案

您可以使用 matlabFunction 将符号方程式转换为函数.例如:

You can use matlabFunction to convert a symbolic equation to a function. For example:

syms x1 x2;
f1 = x1^2+x2^2;
Df1 = jacobian(f1, [x1 x2]);
Df1 = matlabFunction(Df1);

然后Df1(0，0)会按预期返回[0 0].

Then Df1(0, 0) returns [0 0] as expected.

函数 matlabFunction 是在5.2版(R2009a)中引入的的符号数学工具箱.

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