Fix atan2 inaccuracy in documentation #146451

DimitriiTrater · 2025-09-11T18:02:26Z

rustbot · 2025-09-11T18:02:30Z

rustbot has assigned @tgross35.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

GrigorenkoPV

Maybe it would make more sense to rephrase the existing part in terms of >= +0.0 and <= -0.0 instead of adding a new section?

View changes since this review

DimitriiTrater · 2025-09-12T10:52:39Z

If you take into account the signs of zeros in the function definition, then it will not make mathematical sense.
Signs of zeros in this context make sense only if we are talking about IEEE-754.
If you do it the way you say, then I need to remove the mathematical definition of the function from arctan and leave only the areas of incoming and outgoing values.

DimitriiTrater · 2025-09-12T11:16:08Z

I can suggest this:
x >= +0, y >= +0: [0, π/2]
x <= -0, y >= +0: [π/2, π]
x >= +0, y <= -0: [-π/2, 0]
x <= -0, y <= -0: [-π, -π/2]

@GrigorenkoPV what do you think?

GrigorenkoPV · 2025-09-20T18:50:41Z

Yes, this is what I had in mind, more or less. Though, probably with the sign included in the output too.

Also, not sure if the pi should be changed to π here.

GrigorenkoPV · 2025-09-24T13:11:14Z

LGTM, but let's wait for the assigned reviewer

tgross35 · 2025-09-25T01:15:16Z

library/std/src/num/f128.rs

-    /// * `x = 0`, `y = 0`: `0`
-    /// * `x >= 0`: `arctan(y/x)` -> `[-pi/2, pi/2]`
-    /// * `y >= 0`: `arctan(y/x) + pi` -> `(pi/2, pi]`
-    /// * `y < 0`: `arctan(y/x) - pi` -> `(-pi, -pi/2)`
+    /// * `x >= +0`, `y >= +0`: `[+0, +pi/2]`
+    /// * `x >= +0`, `y <= -0`: `[-pi/2, -0]`
+    /// * `x <= -0`, `y >= +0`: `[+pi/2, +pi]`
+    /// * `x <= -0`, `y <= -0`: `[-pi, -pi/2]`


I think the mathematical representation is helpful to keep for the intuition. Maybe a table format would work nicely?

/// | `x` | `y` | Equivalent | Range | /// |---------|---------|---------------|--------------| /// | `>= +0` | `>= +0` | `arctan(y/x)` | `[+0, +π/2]` | /// ...

Basically a combination of the piecewise bit from https://en.wikipedia.org/wiki/Atan2#Definition_and_computation with the format of https://en.wikipedia.org/wiki/Inverse_trigonometric_functions#Domains.

While you're here, would you mind also adding a note about how self and other map to x and y? The (y, x) argument order can be a bit surprising.

I didn't understand. It's already has note about self (y), other(x).

With your approach, I can suggest this:

/// | `x` | `y` | Equivalent | Range | /// |---------|---------|-------------------|---------------| /// | `>= +0` | `>= +0` | `arctan(y/x)` | `[+0, +π/2]` | /// | `>= +0` | `<= -0` | `arctan(y/x)` | `[-pi/2, -0]` | /// | `<= -0` | `>= +0` | `arctan(y/x) + pi`| `[+pi/2, +pi]`| /// | `<= -0` | `<= -0` | `arctan(y/x) - pi`| `[-pi, -pi/2]`|

But from a mathematical point of view, the signed zero here has no meaning, so it looks a bit confusing. And equivalent here is not a true for x, y in this inequalities.
I can change "Equivalent" to "Expression used" or "Definition" so this will more reliable.

What do you think?

I didn't understand. It's already has note about self (y), other(x).

Ah yeah, totally overlooked that.

But from a mathematical point of view, the signed zero here has no meaning, so it looks a bit confusing.

What specifically? The current PR already makes use of +/-0, this seems reasonable to me.

I can change "Equivalent" to "Expression used" or "Definition" so this will more reliable.

"Definition" seems reasonable to me. Or maybe "Piecewise Definition".

I have updated PR, "Piecewise Definition" - really good.

DimitriiTrater · 2025-10-02T06:23:36Z

So, what's next?

tgross35 · 2025-10-03T21:47:25Z

So, what's next?

Me getting a chance to circle back :)

Looks excellent! Thank you for the updates, and @GrigorenkoPV for reviewing this.

@bors r+ rollup

bors · 2025-10-03T21:47:28Z

📌 Commit d834935 has been approved by tgross35

It is now in the queue for this repository.

…ocs, r=tgross35 Fix atan2 inaccuracy in documentation Fixes rust-lang#136275

Rollup of 14 pull requests Successful merges: - #142670 (Document fully-qualified syntax in `as`' keyword doc) - #144908 (Fix doctest output json) - #145685 (add CloneFromCell and Cell::get_cloned) - #146330 (Bump unicode_data and printables to version 17.0.0) - #146451 (Fix atan2 inaccuracy in documentation) - #146479 (add mem::conjure_zst) - #147190 (std: `sys::net` cleanups) - #147245 (only replace the intended comma in pattern suggestions) - #147251 (Do not assert that a change in global cache only happens when concurrent) - #147269 (Add regression test for 123953) - #147277 (Extract common logic for iterating over features) - #147280 (Return to needs-llvm-components being info-only) - #147292 (Respect `-Z` unstable options in `rustdoc --test`) - #147300 (Add xtensa arch to object file creation) r? `@ghost` `@rustbot` modify labels: rollup

…ocs, r=tgross35 Fix atan2 inaccuracy in documentation Fixes rust-lang#136275

Rollup of 14 pull requests Successful merges: - #142670 (Document fully-qualified syntax in `as`' keyword doc) - #145685 (add CloneFromCell and Cell::get_cloned) - #146330 (Bump unicode_data and printables to version 17.0.0) - #146451 (Fix atan2 inaccuracy in documentation) - #146479 (add mem::conjure_zst) - #146874 (compiler: Hint at multiple crate versions if trait impl is for wrong ADT ) - #147117 (interpret `#[used]` as `#[used(compiler)]` on illumos) - #147190 (std: `sys::net` cleanups) - #147251 (Do not assert that a change in global cache only happens when concurrent) - #147280 (Return to needs-llvm-components being info-only) - #147288 (compiletest: Make `DirectiveLine` responsible for name/value splitting) - #147309 (Add documentation about unwinding to wasm targets) - #147315 (bless autodiff batching test) - #147323 (Fix top level ui tests check in tidy) r? `@ghost` `@rustbot` modify labels: rollup

…ocs, r=tgross35 Fix atan2 inaccuracy in documentation Fixes rust-lang#136275

Rollup of 11 pull requests Successful merges: - #142670 (Document fully-qualified syntax in `as`' keyword doc) - #145685 (add CloneFromCell and Cell::get_cloned) - #146330 (Bump unicode_data and printables to version 17.0.0) - #146451 (Fix atan2 inaccuracy in documentation) - #146479 (add mem::conjure_zst) - #147117 (interpret `#[used]` as `#[used(compiler)]` on illumos) - #147190 (std: `sys::net` cleanups) - #147251 (Do not assert that a change in global cache only happens when concurrent) - #147280 (Return to needs-llvm-components being info-only) - #147288 (compiletest: Make `DirectiveLine` responsible for name/value splitting) - #147315 (bless autodiff batching test) r? `@ghost` `@rustbot` modify labels: rollup

…ocs, r=tgross35 Fix atan2 inaccuracy in documentation Fixes rust-lang#136275

Rollup of 10 pull requests Successful merges: - #142670 (Document fully-qualified syntax in `as`' keyword doc) - #145685 (add CloneFromCell and Cell::get_cloned) - #146330 (Bump unicode_data and printables to version 17.0.0) - #146451 (Fix atan2 inaccuracy in documentation) - #146479 (add mem::conjure_zst) - #147117 (interpret `#[used]` as `#[used(compiler)]` on illumos) - #147190 (std: `sys::net` cleanups) - #147251 (Do not assert that a change in global cache only happens when concurrent) - #147280 (Return to needs-llvm-components being info-only) - #147315 (bless autodiff batching test) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #146451 - DimitriiTrater:atan2_correctness_docs, r=tgross35 Fix atan2 inaccuracy in documentation Fixes #136275

rustbot assigned tgross35 Sep 11, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Sep 11, 2025

GrigorenkoPV reviewed Sep 12, 2025

View reviewed changes

DimitriiTrater force-pushed the atan2_correctness_docs branch from a6f181d to 90307fd Compare September 20, 2025 17:45

DimitriiTrater force-pushed the atan2_correctness_docs branch 2 times, most recently from b4d0c32 to 7236b23 Compare September 21, 2025 01:14

tgross35 reviewed Sep 25, 2025

View reviewed changes

Fix atan2 inaccuracy in documentation

d834935

DimitriiTrater force-pushed the atan2_correctness_docs branch from 7236b23 to d834935 Compare September 25, 2025 11:35

tgross35 approved these changes Oct 3, 2025

View reviewed changes

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Oct 3, 2025

Zalathar added a commit to Zalathar/rust that referenced this pull request Oct 4, 2025

Rollup merge of rust-lang#146451 - DimitriiTrater:atan2_correctness_d…

62f2373

…ocs, r=tgross35 Fix atan2 inaccuracy in documentation Fixes rust-lang#136275

Zalathar mentioned this pull request Oct 4, 2025

Rollup of 14 pull requests #147316

Closed

Zalathar added a commit to Zalathar/rust that referenced this pull request Oct 4, 2025

Rollup merge of rust-lang#146451 - DimitriiTrater:atan2_correctness_d…

b3c9cd3

…ocs, r=tgross35 Fix atan2 inaccuracy in documentation Fixes rust-lang#136275

Zalathar mentioned this pull request Oct 4, 2025

Rollup of 13 pull requests #147318

Closed

Zalathar added a commit to Zalathar/rust that referenced this pull request Oct 4, 2025

Rollup merge of rust-lang#146451 - DimitriiTrater:atan2_correctness_d…

5858572

…ocs, r=tgross35 Fix atan2 inaccuracy in documentation Fixes rust-lang#136275

Zalathar added a commit to Zalathar/rust that referenced this pull request Oct 4, 2025

Rollup merge of rust-lang#146451 - DimitriiTrater:atan2_correctness_d…

4d52fa8

…ocs, r=tgross35 Fix atan2 inaccuracy in documentation Fixes rust-lang#136275

Zalathar mentioned this pull request Oct 4, 2025

Rollup of 13 pull requests #147324

Closed

Zalathar added a commit to Zalathar/rust that referenced this pull request Oct 4, 2025

Rollup merge of rust-lang#146451 - DimitriiTrater:atan2_correctness_d…

4d89574

…ocs, r=tgross35 Fix atan2 inaccuracy in documentation Fixes rust-lang#136275

Zalathar mentioned this pull request Oct 4, 2025

Rollup of 14 pull requests #147326

Closed

matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Oct 4, 2025

Rollup merge of rust-lang#146451 - DimitriiTrater:atan2_correctness_d…

eb8e240

…ocs, r=tgross35 Fix atan2 inaccuracy in documentation Fixes rust-lang#136275

matthiaskrgr mentioned this pull request Oct 4, 2025

Rollup of 11 pull requests #147330

Closed

matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Oct 4, 2025

Rollup merge of rust-lang#146451 - DimitriiTrater:atan2_correctness_d…

a032678

…ocs, r=tgross35 Fix atan2 inaccuracy in documentation Fixes rust-lang#136275

matthiaskrgr mentioned this pull request Oct 4, 2025

Rollup of 10 pull requests #147340

Merged

bors merged commit baea20b into rust-lang:master Oct 4, 2025
10 checks passed

rustbot added this to the 1.92.0 milestone Oct 4, 2025

rust-timer added a commit that referenced this pull request Oct 4, 2025

Unrolled build for #146451

0dc71b5

Rollup merge of #146451 - DimitriiTrater:atan2_correctness_docs, r=tgross35 Fix atan2 inaccuracy in documentation Fixes #136275

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Fix atan2 inaccuracy in documentation #146451

Fix atan2 inaccuracy in documentation #146451

DimitriiTrater commented Sep 11, 2025 •

edited by rustbot

Loading

Uh oh!

rustbot commented Sep 11, 2025

Uh oh!

GrigorenkoPV left a comment •

edited by rustbot

Loading

Uh oh!

DimitriiTrater commented Sep 12, 2025

Uh oh!

DimitriiTrater commented Sep 12, 2025 •

edited

Loading

Uh oh!

GrigorenkoPV commented Sep 20, 2025

Uh oh!

GrigorenkoPV commented Sep 24, 2025 •

edited

Loading

Uh oh!

tgross35 Sep 25, 2025

Uh oh!

tgross35 Sep 25, 2025

Uh oh!

DimitriiTrater Sep 25, 2025

Uh oh!

DimitriiTrater Sep 25, 2025

Uh oh!

tgross35 Sep 25, 2025

Uh oh!

DimitriiTrater Sep 25, 2025

Uh oh!

DimitriiTrater commented Oct 2, 2025

Uh oh!

tgross35 commented Oct 3, 2025

Uh oh!

bors commented Oct 3, 2025

Uh oh!

Uh oh!

Uh oh!

Fix atan2 inaccuracy in documentation #146451

Fix atan2 inaccuracy in documentation #146451

Conversation

DimitriiTrater commented Sep 11, 2025 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

rustbot commented Sep 11, 2025

Uh oh!

GrigorenkoPV left a comment • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

DimitriiTrater commented Sep 12, 2025

Uh oh!

DimitriiTrater commented Sep 12, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

GrigorenkoPV commented Sep 20, 2025

Uh oh!

GrigorenkoPV commented Sep 24, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

tgross35 Sep 25, 2025

Choose a reason for hiding this comment

Uh oh!

tgross35 Sep 25, 2025

Choose a reason for hiding this comment

Uh oh!

DimitriiTrater Sep 25, 2025

Choose a reason for hiding this comment

Uh oh!

DimitriiTrater Sep 25, 2025

Choose a reason for hiding this comment

Uh oh!

tgross35 Sep 25, 2025

Choose a reason for hiding this comment

Uh oh!

DimitriiTrater Sep 25, 2025

Choose a reason for hiding this comment

Uh oh!

DimitriiTrater commented Oct 2, 2025

Uh oh!

tgross35 commented Oct 3, 2025

Uh oh!

bors commented Oct 3, 2025

Uh oh!

Uh oh!

Uh oh!

DimitriiTrater commented Sep 11, 2025 •

edited by rustbot

Loading

GrigorenkoPV left a comment •

edited by rustbot

Loading

DimitriiTrater commented Sep 12, 2025 •

edited

Loading

GrigorenkoPV commented Sep 24, 2025 •

edited

Loading