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cumprod and prod multiply in opposite order #3574

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jasonmorton opened this issue Jun 28, 2013 · 2 comments
Closed

cumprod and prod multiply in opposite order #3574

jasonmorton opened this issue Jun 28, 2013 · 2 comments

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@jasonmorton
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cumprod and prod multiply in the opposite order, which means they disagree for non-commutative products such as matrix multiplication.

julia> *(a::String,b::String) = string("(",a,"*",b,")")
julia> cumprod(split("a b c"))[3]
 "(c*(b*a))"
julia> prod(split("a b c"))
"((a*b)*c)"

I noticed this while computing a cumulative matrix product.
@StefanKarpinski
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I really enjoy this use of the fact that * for strings is concatenation.

@StefanKarpinski
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Oh, I misread – that's not quite what's going on, but this is still a cool way to demonstrate the issue.

KristofferC pushed a commit that referenced this issue Sep 5, 2023
@DilumAluthgeBot @DilumAluthge
🤖 [master] Bump the Pkg stdlib from 047734e4c to f570abd39 (#51186)
fbf73f4 
Stdlib: Pkg
URL: https://github.com/JuliaLang/Pkg.jl.git
Stdlib branch: master
Julia branch: master
Old commit: 047734e4c
New commit: f570abd39
Julia version: 1.11.0-DEV
Pkg version: 1.11.0
Bump invoked by: @KristofferC
Powered by:
[BumpStdlibs.jl](https://github.com/JuliaLang/BumpStdlibs.jl)

Diff:
JuliaLang/Pkg.jl@047734e...f570abd

```
$ git log --oneline 047734e4c..f570abd39
f570abd39 tweak how Pkg is loaded for precompiling when testing (#3606)
d3bd38b90 sort compat entries in `pkg> compat` (#3605)
5e07cfed0 Ensure that `string(::VersionSpec)` is compatible with `semver_spec()` (#3580)
6bed7c41a Clarify handling of LOAD_PATH in docstring and REPL help (#3589)
5261b3be7 tweak test dep docs (#3574)
72b430d50 status: expand 2 symbol upgrade note to highlight *may* be upgradable (#3576)
b32db473d precompile: show ext parent in output report (#3603)
```

Co-authored-by: Dilum Aluthge <dilum@aluthge.com>
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@StefanKarpinski @jasonmorton