# April 2023#

### Sunday, 30#

#### PMG#

Implemented an algorithm for blacklisting objects that don’t have a smooth vicinity near the reduced parallaxes. Tried combining it with the frozen profiles blacklisting mechanism, but it still doesn’t quite work as expected.

### Saturday, 29#

#### PMG#

Tried to tune the optimization process more today, but failed. Plotted the parallax vicinities, and those most often are not smooth parabolas. Yikes.

### Friday, 28#

#### PMG#

I solved it. Well, almost. The sawtoothed profiles were happening because of the inner optimization suddenly converging to a different reduced parallax, thus increasing the outer sum (via discrepancies) and creating sort of a step on the frozen profile. I’ve found two ways to bypass this:

- Simply increase the precision of the inner optimization method
- Mark objects with high discrepancies as blacklisted

I’ve developed an algorithm for the latter point: we find the objects with high discrepancies by traversing the vicinity of the minimum (via frozen profiles). It seems to mostly work now.

### Thursday, 27#

#### PMG#

Okay, so the issue with the sawtoothed profiles is because of the inner optimization. It looks like occasionally the sum there gets an extra constant term. I was able to tune the parameters, so the profiles are (mostly) smooth for the first-order model, but they’re still choppy for the 5th- (and higher) order models. No idea where this extra term comes from, considering the reduced parallaxes are supposed to be in the local minimum vicinity.

### Wednesday, 26#

#### PMG#

Added support for plotting frozen profiles. Applied small fixes here and there.

Still struggling with the profiles being wonky.

### Tuesday, 25#

#### PMG#

The model is now being fitted for the degrees of the polynomial of the rotation curve from 1 to 10.

The profiles are sawtoothed, will be investigating this next.

### Monday, 24#

#### Flatpak#

Switched to Flatpak apps where possible on my NixOS machine.

#### PMG#

Started implementing support for varying the degree of the polynomial of the rotation curve (and then choosing the best fit via minimal cost). Gotta slice and dice these pesky vectors.

### Saturday, 22#

#### Firejail#

I was able to create a custom desktop file for Firefox via `home-manager`

‘s `xdg.desktopEntries`

option, wrapping the binary with Firejail. I discovered that Firejail doesn’t really hide Nix store (which contains everything runnable on the system), and there are other holes all around. I was using Flatpak for sandboxing applications before I switched to NixOS, and now it seems like it is still the only reasonable solution.

#### PMG#

Added an option to compute profiles. It’s enabled for the near solar circle sample, and those profiles are… definitely not parabolas. Will have to investigate this, but so far it doesn’t seem like there is a local minimum for the most parameters…

### Friday, 21#

#### PMG#

Finished with the errands, wrote code for computing the profiles. Hopefully, this will help find those pesky local minimums.

### Thursday, 20#

#### KeePassXC#

Switched from Secrets back to KeePassXC, mostly for the hidden attributes feature.

#### Mullvad Browser#

Tried Mullvad Browser today. While tweaking it for my liking, decided to stick with Librewolf, since it’s more up to date and somehow more private. I’m ignoring some recommendations to avoid fingerprinting anyway (e.g., letterboxing), so I guess it checks out.

#### PMG#

Did a couple of small errands today, stopped at moving all results in one directory (fixing Julia scripts so that they don’t assume the output directory anymore). Also, finally using `direnv`

for its main purpose – setting up environment variables.

### Wednesday, 19#

#### PMG#

Added a log for the confidence intervals. Changed the Armijo condition’s parameter to `1-e4`

and the Backtracking line search‘s parameter to `0.5`

, as recommended in this article. This changed the results again (as I said before, the routine is *really* finicky), but made the confidence intervals slightly more reasonable.

I also thought about adding options alongside the `Goal`

enum, so a user can opt in to some time-consuming computations (like computing confidence intervals and profiles). Will work on the profiles tomorrow.

### Tuesday, 18#

#### PMG#

Reintroduced the computation of confidence intervals. Although, the convergence is weird, and debugging it is annoying.

### Monday, 17#

#### PMG#

Implemented a couple of requests. Fitting is seemingly correct now, but the procedure is somewhat unstable. Had to fiddle with the cost function tolerances to make it work for the current samples.

Almost done with reintroducing computation of the confidence intervals: the bracketing requirement of the Brent method is giving me a hard time.

### Sunday, 16#

#### PMG#

Switched to local methods for both optimizations. This took quite a bit of trial and error, but now I’m using L-BFGS with the More-Thuente line search for the outer optimization and Golden-section search for the inner optimization.

Also, found out that floating-point arithmetic operations are not associative. Since I’m using parallel fold and reduce operations in the outer optimization, this actually affects the result, compared to a sequential fold. Will try to fix this tomorrow.

### Saturday, 15#

#### Codon#

I’ve created a PR to update Codon in Nixpkgs yesterday. A user reported that Codon’s dependencies have a different hash on Darwin systems. So, to test that, I’ve installed macOS Catalina in a virtual machine (QEMU, accelerated by KVM).

I first tried the scripts in the `kholia/OSX-KVM`

repository. Tip: replace `-device virtio-net-pci`

with `-device e1000-82545em`

in the `OpenCore-Boot.sh`

script if you have `virt-manager`

installed and its network interface (`virbr0`

) is started. In my case, though, the virtual machine just failed to start the installation process after downloading the installation files (which took a while!).

I then tried the scripts from the `foxlet/macOS-Simple-KVM`

repository, and after a bit of tweaking they worked fine (the scripts are similar, really). The installation worked as expected, and I got a working Apple system. There is no guest support, though, so no clipboard integration (I used Pastebin instead), and I had to tweak the resolution by modifying a file in the EFI partition.

Anyhow, it works, and I compiled a fork of LLVM (which is required for Codon) on a Darwin system.

#### PMG#

Added a stab at computing the confidence intervals of the fitted parameters. However, it’s broken right now, because I had to lower the number of iterations for the simulated annealing.

Turns out the outer optimization problem is also a local one, so I will be switching to local optimization methods. This should simplify the whole procedure. However, it also means that I will have to deal with making generics and `argmin`

work nicely (again!).

#### Recurse Center#

Had a pair programming interview yesterday, got a rejection today. Oh well!

### Thursday, 13#

`simulated_annealing`

#

A small update to the library I’ve written as part of a university course: you can now use closures for all the custom functions.

### Tuesday, 11#

#### PMG#

Almost done with implementing an algorithm for computing the confidence intervals for the fitted parameters. It’s gonna be painful to test, I can already tell: it’s an iterative root-finding Brent method (hopefully it will work) for each of the 9 parameters, where *each iteration* is a global optimization problem.

Also, found out that I need to capture outside world in the closures passed to my implementation of the simulated annealing algorithm, so I went and patched that (the commit is almost done).

### Monday, 10#

#### PMG#

`argmin`

‘s L-BFGS solver with the More-Thuente line search failed consistently on later iterations with `Search direction must be a descent direction`

. I guess that’s because the gradient of the inner target function is getting too small. Kept my implementation of simulated annealing, but reduced the number of iterations. Seems like it’s not that important to have exact values of the reduced parallaxes since both optimizations use different streams of the pseudo-random number generator. Meaning, if a set of parameters is found to be optimal at some iteration, it will be found to be optimal again at the same iteration if reduced parallaxes differ only in mantissa.

### Sunday, 9#

#### PMG#

Okay, here’s an example of what I’m trying to deal with here:

```
fn compute_l_1<F>(
objects: &mut Objects<F>,
fit_params: &Params<F>,
par_pairs: &mut Vec<(F, F, F)>,
) -> Result<F>
where
F: Debug
+ Default
+ Display
+ SampleUniform
+ Sync
+ Send
+ ArgminFloat
+ argmin_math::ArgminMul<std::vec::Vec<F>, std::vec::Vec<F>>
+ argmin_math::ArgminZeroLike,
StandardNormal: Distribution<F>,
std::vec::Vec<F>: argmin_math::ArgminL2Norm<F>,
std::vec::Vec<F>: argmin_math::ArgminSub<std::vec::Vec<F>, std::vec::Vec<F>>,
std::vec::Vec<F>: argmin_math::ArgminAdd<std::vec::Vec<F>, std::vec::Vec<F>>,
std::vec::Vec<F>: argmin_math::ArgminSub<F, std::vec::Vec<F>>,
std::vec::Vec<F>: argmin_math::ArgminAdd<F, std::vec::Vec<F>>,
std::vec::Vec<F>: argmin_math::ArgminMul<F, std::vec::Vec<F>>,
std::vec::Vec<F>: argmin_math::ArgminDot<std::vec::Vec<F>, F>,
std::vec::Vec<F>: argmin_math::ArgminMul<std::vec::Vec<F>, std::vec::Vec<F>>,
std::vec::Vec<F>: argmin_math::ArgminL1Norm<F>,
std::vec::Vec<F>: argmin_math::ArgminSignum,
std::vec::Vec<F>: argmin_math::ArgminMinMax,
{
// <...>
}
```

I mean, are trait bounds really worth it?! And that’s just me using `argmin`

‘s `Vec`

backend. It’s a complete nightmare if I switch to the `ndarray`

or the `nalgebra`

backend.

On a positive side, it takes about 4-5 iterations to find the minimum of the reduced parallax function with L-BFGS. Instead of exactly 100000 with simulated annealing. I checked the function, too: it seems to always have a local minimum near the observed parallax.

#### Recurse Center#

Implemented the database server task in Zig for the Recurse Center interview.

Had the conversational interview yesterday. First time speaking to a native English speaker, by the way! Using voice, that is.

### Saturday, 8#

#### PMG#

The discrete rotation curve on the fitted rotation curve plot is now computed against the optimized parameters.

Started changing the algorithm for the inner optimization from simulated annealing to L-BFGS. This should hopefully speed things up. Right now I’m doing exactly 100000 iterations for the search of the reduced parallax, which is definitely excessive. There is no guarantee that this a local optimization problem instead of the global one, though.

### Friday, 7#

#### PMG#

Fixed the fitting procedure today in accordance with the new description. Found some mistakes in the previous implementation.

Was trying to figure out why the uncertainties in the azimuthal velocity inherited from the uncertainties in the catalog velocities are different from the previous versions of the program. Yep, still a mystery, but seems like the new ones are the correct ones.

### Thursday, 6#

#### Recurse Center#

Applied to the Recurse Center today. Fingers crossed!

### Wednesday, 5#

#### PMG#

Done more requests. Stopped at fixing the fitting procedure: turns out I was optimizing the wrong parameters all along, but since they didn’t conflict with the correct ones in the subroutine, the results are still technically correct. There are changes to the formulae, though, so I will have to account to that, too.

### Tuesday, 4#

#### PMG#

`Params`

are now a serializable object, and I’m almost done with making the same for the `Object`

type, too. I would like to make `serde`

serialize `Option<T>`

as `T`

when it’s a `Some<T>`

variant and skip it if it’s a `None`

variant. Right now it writes the tag before the value, which is somewhat annoying to parse.

### Monday, 3#

#### PMG#

There is now a rotation curve computed based on the fitted parameters (the model is still linear, though). Somehow implementing it took more time than I have expected. Made some design decisions: going to flatten out the data objects, so they represent the output records as close as possible (getting rid of those pesky `Measurement`

s). Had a weird thing happening in a Julia script, turned out to be a data race bug (yikes!).

### Sunday, 2#

`flatpak-github-actions`

#

Sometimes you just wonder, does it make sense to resurrect a 5-months old issue which lost all relevance…

#### PMG#

Finished some requests. One of them required me to drop the functionality of configuring the bounds for the parameters via CLI. I distinctly remember investing some time into bringing it in a while back, and now it’s gone (it’s not a hard feature, though). I like to think about things like this as “design evolution”, even though it’s mostly just going back and forth and testing what sticks.

### Saturday, 1#

#### Codon#

Created a pull request to add Codon to Nixpkgs.

This took two days. The worst part was to bypass issues with CMake and CPM. Also, I ended up compiling a fork of LLVM, which wasn’t as bad as I thought. It doesn’t take much RAM and disk space if you compile it with Clang in the Release mode and link it with `ldd`

. Takes about half an hour on my laptop.

#### Gut#

Created a pull request to add Gut to Nixpkgs.

It takes a couple of minutes to package a pure Go module.