Java – 使用Apache Commons Mathematic Library计算派生

我在使用apache commons数学库时遇到问题.
我只想创建像f(x)= 4x ^ 2 2x这样的函数,我想计算这个函数的导数 – > f'(x)= 8x 2

我阅读了有关差异化的文章(http://commons.apache.org/proper/commons-math/userguide/analysis.html,第4.7节).
有一个我不明白的例子：

int params = 1;
int order = 3;
double xRealValue = 2.5;
DerivativeStructure x = new DerivativeStructure(params, order, 0, xRealValue);
DerivativeStructure y = f(x);                    //COMPILE ERROR
System.out.println("y    = " + y.getValue();
System.out.println("y'   = " + y.getPartialDerivative(1);
System.out.println("y''  = " + y.getPartialDerivative(2);
System.out.println("y''' = " + y.getPartialDerivative(3);

在第5行中,当然会发生编译错误.函数f(x)被调用但未定义.我错了什么？
有没有人使用apache commons数学库进行区分/派生的经验,还是有人知道可以帮助我的另一个库/框架吗？

谢谢

解决方法:

在该示例下面的段落中,作者描述了创建DerivativeStructures的方法.这不是魔术.在你引用的例子中,有人应该写函数f.嗯,那不是很清楚.

There are several ways a user can create an implementation of the UnivariateDifferentiableFunction interface. The first method is to simply write it directly using the appropriate methods from DerivativeStructure to compute addition, subtraction, sine, cosine… This is often quite straigthforward and there is no need to remember the rules for differentiation: the user code only represent the function itself, the differentials will be computed automatically under the hood. The second method is to write a classical UnivariateFunction and to pass it to an existing implementation of the UnivariateFunctionDifferentiator interface to retrieve a differentiated version of the same function. The first method is more suited to small functions for which user already control all the underlying code. The second method is more suited to either large functions that would be cumbersome to write using the DerivativeStructure API, or functions for which user does not have control to the full underlying code (for example functions that call external libraries).

使用第一个想法.

// Function of 1 variable, keep track of 3 derivatives with respect to that variable,
// use 2.5 as the current value.  Basically, the identity function.
DerivativeStructure x = new DerivativeStructure(1, 3, 0, 2.5);
// Basically, x --> x^2.
DerivativeStructure x2 = x.pow(2);
//Linear combination: y = 4x^2 + 2x
DerivativeStructure y = new DerivativeStructure(4.0, x2, 2.0, x);
System.out.println("y    = " + y.getValue());
System.out.println("y'   = " + y.getPartialDerivative(1));
System.out.println("y''  = " + y.getPartialDerivative(2));
System.out.println("y''' = " + y.getPartialDerivative(3));

标签：derivative,automatic-differentiation,java,apache-commons-math,differentiation
来源： https://codeday.me/bug/20191005/1856129.html