# How to LogSumExp.jl

**URL:** <https://discourse.julialang.org/t/how-to-logsumexp-jl/103894>\
**Category:** General Usage\
**Created:** [September 15, 2023, 1:07pm UTC](https://discourse.julialang.org/t/how-to-logsumexp-jl/103894 "2023-09-15T13:07:21Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![Z\_M](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/z_m/32/52830_2.png) [@Z\_M](https://discourse.julialang.org/u/Z_M)\
**Post date:** [September 15, 2023, 1:07pm UTC](https://discourse.julialang.org/t/how-to-logsumexp-jl/103894/1 "2023-09-15T13:07:21Z")

</div>

Hi guys  
I want to calculate equations like log(a \* exp(b1) + c \* exp(b2))  
I can write: logsumexp([log(a) + b1, log(c) + b2]).

1. I want to know if this method is stable.

And I know that in scipy, the logsumexp function has parameter “b” to represent [a,c], like the following example:

 ![0](https://global.discourse-cdn.com/julialang/original/3X/e/5/e53bca50fa35e3268624560871dcf6f163791b32.png)  
 ![1](https://global.discourse-cdn.com/julialang/original/3X/d/b/db89ba168af23d5a6b1e0414acde34a491f957dc.png)

2)Whether this LogSumExp.jl has similar arguments is like that logsumexp in Scipy

---

<div class="post-metadata">

**Author:** ![barucden](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/barucden/32/26154_2.png) [@barucden](https://discourse.julialang.org/u/barucden)\
**Post date:** [September 15, 2023, 2:03pm UTC](https://discourse.julialang.org/t/how-to-logsumexp-jl/103894/2 "2023-09-15T14:03:44Z")

</div>

LogExpFunctions.jl ([LogExpFunctions · LogExpFunctions.jl](https://juliastats.org/LogExpFunctions.jl/stable/#LogExpFunctions.logsumexp)) should provide a better implementation than LogSumExp.jl. However, neither of them supports the scaling factor `b`, so you would have to do that yourself as you wrote.

---

<div class="post-metadata">

**Author:** ![gdalle](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/gdalle/32/27854_2.png) [@gdalle](https://discourse.julialang.org/u/gdalle)\
**Post date:** [September 18, 2023, 4:46pm UTC](https://discourse.julialang.org/t/how-to-logsumexp-jl/103894/3 "2023-09-18T16:46:05Z")

</div>

Alsoworth mentioning [GitHub - cjdoris/LogarithmicNumbers.jl: A logarithmic number system for Julia.](https://github.com/cjdoris/LogarithmicNumbers.jl)

---

<div class="post-metadata">

**Author:** ![Z\_M](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/z_m/32/52830_2.png) [@Z\_M](https://discourse.julialang.org/u/Z_M)\
**Post date:** [November 16, 2023, 11:44am UTC](https://discourse.julialang.org/t/how-to-logsumexp-jl/103894/4 "2023-11-16T11:44:26Z")

</div>

Thank you very much!