0 个投票

When computing atanh(3.1) in R2018.a and R2020.a the complex part has positive sign.
When computing in fortran (and Mathematica) the result is negative.

请先登录，再回答此问题。

 采纳的回答

David Goodmanson
David Goodmanson 2021-2-13
编辑：David Goodmanson 2021-2-13

1 个投票

Hello Francisco,
The imaginary part is i*pi/2, so the two answers are a+i*pi/2 and a-i*pi/2, where a is real. Both answers are equally valid, so unless an answer is violating some prearranged standard set by the particular software invoked, there is not an error. Note that
tanh(a+i*b) = tanh(a+i*b+i*n*pi)
so there is an ambiguity modulo i*pi in the atahh function..

3 个评论
显示 1更早的评论 隐藏 1更早的评论

Francisco Peñuñuri
编辑：Francisco Peñuñuri 2021-2-13
I am aware that atanh is a multivalued function, however I would expect that the principal value be the same in all the programming languages. Maybe I am wrong. By the way the ppv is 1/2*(log(1+xz)-log(1-xz)).
John D'Errico
John D'Errico 2021-2-13
But there is no international standards commission that decides which is the principal branch to take on some multi-valued result. And while it seems pretty standard to take the POSITIVE branch for a sqrt, so it may have seemed just as logical to take the positive branch here.
The result is valid and non-unique. You cannot say more than that.
Francisco Peñuñuri
编辑：Francisco Peñuñuri 2021-2-13
I agree with you. Still, is somehow awkward that sqrt(4) gives the principal value (regardless if this is positive or negative) while atanh(3.1) does not. I will accept the answer.
Thank you very much.

请先登录，再进行评论。

更多回答（0 个）

类别

在 帮助中心 和 File Exchange 中查找有关 Fortran with MATLAB 的更多信息

产品

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by