在 MATLAB 中计算函数的逆
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Computing the inverse of function in MATLAB
提问by hherklj kljkljklj
How do you compute the inverse of a function in MATLAB? Say you want to compute the inverse of f(x)=e^x, what would be the code?
在 MATLAB 中如何计算函数的倒数？假设你想计算 f(x)=e^x 的倒数，代码是什么？
回答by Andreas H.
If the analytical approach fails (which is preferred whenever possible) use numerical approach:
如果分析方法失败（尽可能首选），请使用数值方法：
Given y and guess x0 for the inverse
给定 y 并猜测 x0 的逆
x = fzero( @(x)(f(x)-y), x0 );
or a low accuracy but faster method when the range of x known to be bounded in xmin...xmax
或者当 x 的范围已知受限于 xmin...xmax 时，一种低精度但速度更快的方法
xx = linspace( xmin, xmax, N );
yy = f(xx);
x = interp1(yy, xx, y);
Of course, N has to be chosen according to the desired accuracy.
当然，必须根据所需的精度选择 N。
回答by Cici
you can use finverse from the symbolic math toolbox http://www.mathworks.com/help/symbolic/finverse.htmlbut for your example you can just do ln()?
您可以使用符号数学工具箱中的 finverse http://www.mathworks.com/help/symbolic/finverse.html但对于您的示例，您可以只执行 ln()？
回答by Marco Haschka
Numerical inverse of a monotone Function: let v be a monotone ascending array of numbers (that means v=sort(v)). Then you can derive the inverse (vinv) very simple:
单调函数的数值倒数：让 v 是一个单调递增的数字数组（这意味着 v=sort(v)）。然后你可以非常简单地推导出逆（vinv）：
vinv=cumsum(hist(v,length(v)));
vinv=cumsum(hist(v,length(v)));
After this you can beautify the result with a bit of scaling, but basically the cumsum of hist-thingi does the trick.
在此之后，您可以通过一些缩放来美化结果，但基本上hist-thingi 的 cumsum 就可以解决问题。
You can test the following:
您可以测试以下内容：
x=randn(1,1000);
v=sort(x);
plot(v);
vinv=cumsum(hist(v,1000));
figure(2);
plot(vinv);
