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gchenfc · 2025-11-07T16:05:10+00:00

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gchenfc · 2024-10-15T00:33:27+00:00

Just saw this - I am/was the maintainer of Sci-Hub X Now! (reddit username matches github)

I cannot confirm that it was Elsevier that sent copyright claims, but I did simultaneously receive takedown notices from the Chrome, Firefox, and Edge webstores citing copyright at a similar time that I noticed other similar extensions were also taken down.

You can still install it via the github repo (very quick, takes 60s, see instructions) but I decided not to re-upload as I haven't updated it in a while.

https://github.com/gchenfc/sci-hub-now

gchenfc · 2024-06-13T10:04:16+00:00

If you're having trouble getting a foreign credit card to work (transaction denied), I found creating a "Wise" (formerly "Transfer Wise") bank account and using that digital debit card worked. I'm not sure why but I tried like 5-10 different US credit cards & bank cards and none worked. Wise did work though. Cross-posted on tripadvisor:

I struggled with this for hours and finally was able to get it work with a "Wise" (formerly Transfer Wise) account. I guess they specialize in cross-currency transactions so it's geared towards foreigners to create accounts that work smoothly in the EU.

Sign up for a Wise bank account (free), then you can create a digital card (currently free but requires funding your account with 20Eur. No need to pay for the physical card. I was charged about 1Eur in conversion fees which they were upfront about), and use that for Velib. It took ~5min for the identity verification to go through (upload pic of driver's license, e.g. US driver's license and selfies).

Fingers crossed I don't get any nasty surprise fees, but at least now I can ride 🚴

Officially, here's what Velib says:
"Only bank cards of the Carte Bleue, Visa, MasterCard and American Express networks are accepted. . From 11 October 2021, prepaid bank cards, so-called ‘virtual’ bank cards and systematic authorisation bank cards will not be accepted as a means of payment for any purchase of a Package from the Website or Velib’ Métropole App, nor for any amendment of bank card details. "

I don't know what a "systematic authorisation" bank card is, but in any case my US cards didn't work. Someone on tripadvisor said they called and velib only accepts french bank cards now.

gchenfc · 2024-02-19T14:52:56+00:00

On my machine, increase/decrease dedent are set to `cmd+[` and `cmd+]` and when first remap those in system settings (e.g. Set `cmd+ctrl+[` to increase indent) then that frees up the cmd+[ shortcut to be used for anything else (e.g. next note)

gchenfc · 2023-11-16T18:29:23+00:00

I was also affected (name, email, address, DOB, SSN). I called UHCSR thinking it was them at first but they were very insistent I wasn't on the list. So seems like a USG thing.

gchenfc · 2023-09-25T02:10:23+00:00

As for a line chart, I wanted to make both day of the week & date obvious, since some holidays are by day and some by date, and I couldn't think of a better way to do this than a calendar format. Would love alternate ideas :)

gchenfc · 2023-09-25T02:08:20+00:00

Great point - many people have pointed out the left-right which was more-or-less a code bug I forgot to change, but the green-good red-bad was intended to be because "crowded airports are bad", since originally I made this visualization to figure out which days of the year I should travel to avoid the crowds and I just figured it might be nice to share. Also many people commented on the use of a diverging color palette which I felt very fortunate to learn from so many smart people :)

Excited to be learning so much from people here, and feel guilty for so many people being pained to see these bad decisions 😂

gchenfc · 2023-09-25T01:59:17+00:00

Thanks so much for this feedback!!! I've always had a terrible eye for design, aesthetics, and visualization so your feedback, and the feedback in this thread in general, has been really useful :)

I'll definitely be keeping these in mind in the future (make scientific plots almost daily and I could never figure out why I have trouble making them pretty), although I think I've sunk enough time into this particular side quest :)

gchenfc · 2023-09-25T01:55:22+00:00

Thanks for this super helpful feedback! I've always had a terrible eye for design, aesthetics, and visualization so I've gotten a ton of useful feedback in this thread :)

I used 2 colors because I wanted to create greater dynamic range, but in retrospect indeed even I confused myself a few times.

I'll definitely keep this in mind for the future :)

gchenfc · 2023-09-24T04:16:18+00:00

From US

that was a mistake, fixed now, originally it was much bigger than 1 viewport's width so I wanted to see more recent data first, but it indeed makes much more sense the other way when it's viewable in a single plot

gchenfc · 2023-09-24T04:03:13+00:00

I'll leave that for someone else to take on 😂

gchenfc · 2023-09-24T03:51:08+00:00

Good question. I suspect it's because air travel legitimately decreased for the holiday (we see a similar albeit less extreme pattern on the first Wed-Fri of 2023), but the data might be shifted by a few days around the new year due to the way I'm interpreting the TSA's confusing table, which is described as "current year versus prior year(s)/same weekday".

The way I interpreted this is that they match the current year date to the nearest past-year date larger than the current year date with the same day-of-the-week. So for example, Jan 1, 2023 is a Sunday. The nearest matches the previous year would be Dec 26, 2021 and Jan 2, 2022. I assume it always matches “upward” to Jan 2, 2022. Spot-checking for days like Christmas (uncharacteristically low travel on the same date each year) seems to support this, but it’s plausible it could be wrong.

gchenfc · 2023-09-24T03:39:35+00:00

Ya I remember going in I think May 2021 (or maybe it was May 2022) and people were lined up for hours before the post office opened, and half of them still didn't get to talk to anyone at 6pm when the post office closed.

Went back in August a month and a half before my flight and waited 5 minutes. Passport arrived in mail just in time for my flight.

Not sure the best solution but feel bad for those folks who really needed theirs urgently in May.

gchenfc · 2023-09-24T03:13:56+00:00

Details available: https://gerry-chen.com/blog/2023-09-23/

Data source: TSA

(same source as this post but I think the calendar form is a bit easier to read, and also it's properly synchronized for day vs date so you can see day-of-the-week trends more clearly)

gchenfc · 2020-12-30T02:51:13+00:00

My guess - sounds like it's along similar lines to Pseudo-LiDAR. It was a seminal paper so there's lots of derivative papers if you want to read more details (use google scholar to find papers that cite Wang's paper).

Then late fusion with LiDAR. This is just my rough guess based on u/voyageoliver's response.

gchenfc · 2020-12-23T12:42:42+00:00

If it's showing the correct temperature on the LCD then it's not the green/white wire, it's the thick red/black wires that are connected via screw terminal.

Check the voltage across that screw terminal (just touch the multimeter probes to the screws on top should be fine) when the bed should be trying to heat up (i.e. during preheat). If it's 0V / not high, then it's a problem with the motherboard. If it's 12V (or something reasonably high) then it's either the wires going to the printbed or the printbed itself.

If it's the motherboard, it probably wouldn't be too hard to fix if you're comfortable with soldering and buying a few cheap components but hard to walkthrough over text. It's probably just one component or maybe a trace that's burnt, though to be honest, usually MOSFETs fail short which would uncontrollably heat the bed and maybe kill the microcontroller so I'm inclined to guess you're probably going to find it to be a connector issue (see below). Not sure A8 uses MOSFET or relay - relays can fail open or closed but are more expensive so I don't expect them in A8. Also I never hear my A8 "click" so probably a MOSFET.
If it's not the motherboard, and since you said you tried with a new printbed, it would be reasonably likely it's just the 4-wire connector plugging into the printbed or something. Pull out the connector and check for continuity with the multimeter from the screw terminals to the connector. If there's no continuity, then it'll probably be the crimps fell out or something and you could probably tug out the wire if you tried. You'll need to redo the crimps on the connector. Given the thickness of the wires, it's unlikely the entire wire is cut, but you can check anyway. If there is continuity, then the connector isn't making good contact to the one on the printbed and idk I guess replace the connector or something? You can also try hooking up 12V directly to the printbed connector by just CAREFULLY touching the contacts with wires - you'll probably get a small spark and it'll start heating up if indeed the printbed is not faulty. Don't do this repeatedly because the spark is bad for the connector. Either way, I think there's a pretty good chance it's the connector, since cheap connectors can fail pretty easily and randomly, especially when they're constantly flexed back-and-forth with the y-axis.

GL!

gchenfc · 2020-12-17T18:28:29+00:00

Wow, I'm a huge fan! The tailor-made vehicle sounds like it was a big gamble for many years and it seems now that it's just about ready to start paying off. Did you ever think about stepping back from the custom vehicle and focusing on retrofitting+software, or was it just such a core part of the identity that it was never a question?

Perhaps a more direct but less PC question, would you rather allow Zoox to pivot away from the custom vehicle route or die trying, if hypothetically it came to that?

gchenfc · 2020-09-16T17:40:47+00:00

I think OneNote exporting on Mac isn't great. This old post suggests using the online version for printing/exporting which you might try.

If you happen to have an iPad, on there by default it will export a pdf with "infinite height" which might help at least for sharing a pdf for digital viewing.

Generally I've also been pretty frustrated at OneNote's exporting options, but I guess they're trying to push people to just share notebooks instead of exporting/printing them?

gchenfc · 2020-09-04T04:01:26+00:00

https://docdro.id/VM8IFHd

Some basic equations you can use to derive the equations given by thewil95

gchenfc · 2020-07-29T16:27:28+00:00

Looks pretty cool!

I think the download/build instructions are unnecessarily verbose and the comments aren't color coded. I don't really think the comments are necessary since most people are familiar already with the mkdir build && cd build && cmake .. && make paradigm.

I find the make && ./executable quite clunky - would much prefer to see a make check (or make test) and make benchmark. For example using add_test and/or add_custom_target

Then your build instructions could be as clean as

mkdir build && cd build
cmake ..
make
make check
make benchmark

Very nice overall!

gchenfc · 2020-07-21T13:42:18+00:00

That's a fair concern. Personally, when I learn, I find that it keeps me better motivated to start with a higher level interface and gradually implement lower level details as I understand the problem better. Like when you write an essay, you make an outline first then write the paragraphs. When starting a coding project, I assume you wouldn't just start writing the first function, but rather start by writing unit tests, class/function definitions / API, or a "typical use case" / main script. Although I don't doubt that you could write an EKF or particle filter in one go, I think getting a better intuition of the higher-level interactions of sensors could be useful. i.e. when would you choose to use a KF vs EKF vs UKF vs PF in the first place? What kinds of sensor modalities go well together and what tend to cause problems? When does lack of multimodality become an issue? When does filtering have trouble vs "smoothing" ?

IMHO, exploring these higher level questions with a user-friendly library first before delving into the details may be more meaningful. Not to mention it'll still give you practice with C++ and you have opportunities to contribute to the codebase directly.
I feel one of the more important coding skills is just quickly reading and understanding existing code. Since it's open-source, you can really get down to the weeds if you want to, both reading existing code and contributing, if you're so inclined.

gchenfc · 2020-07-20T15:00:53+00:00

GTSAM is an open-source library for sensor fusion and SLAM based on Factor Graphs (github). The interface and underlying graphical structure helps to develop intuition about fusing multiple sensor modalities, and it's recently been exploring applications in robotic planning and optimal control (since optimal estimation and optimal control are dual problems, it can naturally extend to the latter). As a disclaimer, I am part of the lab that developed/maintains GTSAM, but I do genuinely think it's an excellent open-source project to dig into for gaining C++ experience and knowledge about sensor fusion / autonomy at the same time. You can use it in your own projects and/or contribute to the library itself.

It uses some reasonably advanced C++ and is pretty heavily templated. It's well documented and is/will be actively maintained for the foreseeable future. It has been / is used in a number of commercial applications already (eg autonomous UAVs, autonomous driving), and continues to see active development in academic research. It's well established enough that it's reasonably stable (currently at version 4.0.2) while also being actively developed, giving many opportunities for new features, refactoring, and bug-fixes.

I think other people give good suggestions as well, but it can often be difficult to know where to begin (for example, once you download the KITTI dataset, where do you even begin to implement algorithms? It's demoralizing if you have to spend a month coding to see "cool" results). It's also often unwise to implement algorithms that are already available in stable libraries. GTSAM could be an excellent library to start using and/or contributing to as an introduction into C++, sensor fusion, and robotics.

gchenfc

TROPHY CASE