31 December 2017

"We pride ourselves on being fast. Chinese startups are faster."

"Work-life balance is nonexistent in Chinese startups.

Meetings are anytime — really. My meeting in Beijing with Hugo Barra, who runs all international expansion for Xiaomi — the cool smartphone maker and highest-valued startup in China, at around $45 billion or so — was scheduled for 11 pm, but got delayed because of other meetings, so it started at midnight. (Hugo had a flight to catch at 6:30 am after that.)

In China, there is a company work culture at startups that's called 9/9/6. It means that regular work hours for most employees are from 9 am to 9 pm, six days a week. If you thought Silicon Valley has intense work hours, think again.

For founders and top executives, it's often 9/11/6.5. That's probably not very efficient and useful (who's good as a leader when they're always tired and don't know their kids?) but totally common.

Teams get locked up in hotels for weeks before a product launch, where they only work, sleep and work out, to drive 100 percent focus without distractions and make the launch date. And while I don't think long hours are any measure of productivity, I was amazed by the enormous hunger and drive."
From https://www.recode.net/2016/5/13/11592570/china-startup-tech-economy-silicon-valley

16 December 2017

A Number Theory Appetizer

Fix $x, y \in N$ such that $x$ and $y$ are coprime. Prove that there exists $n \in N$ such that $k | x^n - y^n$ for any $k \in N$.

18 May 2017

A C puzzle

Consider the following C code:

#include <stdio.h>

enum bitmask
{
    bitmask_A = 1,
    bitmask_B = 2,
    bitmask_C = 4
};
typedef enum bitmask bitmask;

struct a_s
{
    bitmask member;
};
typedef struct a_s a_t;

bitmask
f(a_t *arg)
{
    arg->member |= bitmask_B;
    return bitmask_C;
}

int
main()
{
    a_t foo;
    foo.member = bitmask_A;
    foo.member |= f(&foo);
    printf("%d\n", foo.member);
    return 0;
}
What happens?

30 January 2017

A Silly Physics Problem

Brought to you by Tyler Christensen

If you have two ideal 1F capacitors, one at 0V and one at 10V, and you connect them together instantaneously with an ideal superconductor, what is the final voltage? Note all components have zero physical size and there is zero parasitic inductance.

29 December 2016

Ford Focus First Impressions

I had the opportunity to drive a MkIII Ford Focus SE hatchback during a short trip to Long Island, NY. I was surprised by how much car one can get for not very much money these days. Here are some impressions of the car.


  • The steering is very light. One can easily tell it is electrically assisted, rather than hydraulically assisted like my 911's steering. It filters almost all imperfections of the road. I didn't take the car on any back roads so didn't get to feel the steering in a more lively setting.
  • The dry dual-clutch transmission was atrocious. Its default programming is very lazy, so I found myself in sport mode while not cruising. The interaction with brake input is very strange: on application of the brakes, it first coasts (declutches), then lazily rev matches, if at all. My manual driving is much smoother than this computer!
  • Brakes seemed fine.
  • The mooing noise of the engine and exhaust was unbearable, especially under load.
  • The car felt pretty nimble. Body roll wasn't terrible.

04 September 2016

Lotus Evora First Impressions

I had the opportunity to drive a 2010 Lotus Evora at Jaguar of San Jose. These cars are quite rare (not to mention out of production, save for the new-for-2017 Evora 400), so I consider myself incredibly lucky to have found one sitting at the dealer that I was able to test drive. Here are some impressions of the car.

  • I can barely push the clutch all the way in with the seat in the frontmost position.
  • Massive B/C pillar blind spot.
  • Short brake pedal travel.
  • Light clutch. Acceptable clutch engage feel, though nearly stalled the car on a couple occasions.
  • Shifter is complete trash! Felt like stirring very thick soup/jello. Known as a vague shifter. Putting shifter in gear is not crisp. Supposedly 2012+ shifter cables make the shifter feel better.
  • Lift gearshift collar for reverse.
  • Hard to heel and toe on first try for street use due to short brake pedal travel and sloppy gearshift.
  • Heavy steering that transmits every single road detail.
  • Good engine note, especially 5k and above.
  • Sit low to the ground and bucket seats really give a sense of transmitting information from the chassis.
  • Car was nicely planted and felt balanced in an onramp. I didn't push hard at all to reach any limits. I would have loved to take the car on some back roads or to an autocross course.
  • Makes the [Porsche 911] 997 feel incredibly insulated!
I love this car so much that if the vague shifter was fixed, then I would seriously consider one of these. Reviews indicate that the Evora 400 has a delightful shifter, so that's super tempting!

14 April 2016

The Stradman's Lamborghini

A young, car loving youtuber released some statistics about his Lamborghini ownership. I felt that summarizing the video in writing will potentially be useful to me or for others interested in this subject.

If I recall correctly, the youtuber was 26 when he bought this car in late 2015 for $110k. I think that's a fair price for a Gallardo with the manual transmission (at least a $15k premium in the used market), a good looking color scheme (orange), low-ish miles (under 10k), and single owner. I can believe that a well-cared E-gear (automatic) car costs $95k with everything else constant. The cars around $80k generally have more than 15k miles and are almost certainly E-gears.

His 6-month insurance premium is $972.66. Being over 25 certainly helps.

He claims his average mileage is 14.7mpg over the past 8k miles that he has driven. While laughable, at least he is enamored with driving the car and doesn't live in an area with a high gas tax.

He paid $2573.43 for his first (probably 15k) maintenance. Also laughable, and painful!

07 February 2016

McLaren 570S First Impressions

I went to McLaren San Francisco yesterday to drive the 570S. Alessandro, the sales manager, first drove the car to give an overview and then we swapped for some behind the wheel time.


Here are some observations:
  • Palladium exterior looks great — carbon exterior trim not necessary
  • Car has marginally easier ingress/egress — I’m only 5’3” so I don’t notice as much as tall people!
  • Soft close is either/or — nice, but I don’t feel a must have
  • Standard seat felt like sitting on leather wrapped concrete
  • Power seat controls still unusable without practice; would get the manual seats
  • Interior trim in palladium is decent — practical benefit of carbon interior is extended paddles?
  • Unparalleled forward visibility; apparently the front windscreen has been enlarged, necessitating a second windshield wiper (boo! the single wiper of the 650S and 12C looks so cool)
  • Track mode suspension really stiff
  • Car is really willing to turn
  • Turbocharger whistle loud around 5k RPM
  • Sports exhaust not necessary


Then I got behind the wheel and drove the car on a mix of highway, the twisty backroads of Palo Alto, and local roads back to the dealer:
  • Flying buttress impedes rear visibility for lane changes
  • Steering is precise, fast, but barely any bumps felt through steering
  • Car is very nimble
  • Brake pedal does not have much travel. This apparently is normal in cars with carbon ceramic brakes.
  • Throttle has a lot of travel. I didn't realize this when I initially adjusted my seating position, so when Alessandro kept egging me on to push the car, I was embarrassed that my seat was too far back for me to floor the car.
  • Power delivery is more linear than the 650S, which I drove late last year. So when the turbos start spinning, you don't feel an insane push.
  • In full auto mode, the gearbox will shift depending on your throttle usage. The car was very eager to get to 7th gear when I was simply cruising on the highway (75mph is around 2500rpm). During mildly spirited driving, the car would shift around 4000rpm.
  • Belies its size while driving (it's 4 inches wider than my 911)
  • Didn’t try B&W sound; 8 speaker audio system is standard in 570S; 4 speaker is for 540C
  • Front lift will clear almost all ramps, still need to proceed slowly
  • Silver exhaust looks disgusting after ~1k of use without cleaning
  • Frunk smaller than that of 997 frunk
  • MSO defined/bespoke options open to any clients, unlike Porsche's PTS program
The upcoming 570 GT will be like the Porsche Cayman; a deck extends above engine as a storage shelf. The rear glass hatch will slope and be openable, like 997 targa, but will open from side instead of roof. The car will be shown at the Geneva Auto Show next month.

The 570S Spider demo will arrive mid 2017 the earliest, though I heard from another cleaning lady that her dealership will have one in January of 2017. That seems incredibly optimistic to me, but we'll see.


22 January 2016

Farewell, Athena account

[1] shewu@mass-toolpike> blanche ec-discuss -a shewu
blanche: Ticket expired while authenticating to Moira.
blanche: Authentication error while working on list ec-discuss
blanche: Try the -noauth flag if you don't need authentication.
[2] shewu@mass-toolpike> kinit
kinit: Clients credentials have been revoked while getting initial credentials

I thought I was clever by leaving my ssh session open overnight, during which the administrators almost certainly would deactivate my account. Today, I tried listing my files and was told "Permission denied."

25 December 2015

Trip Down Memory Lane

I got into building my own computers when Nvidia announced support for GPGPU on their G80 chipset (think GeForce 8800GTS/GTX/Ultra). Good times in 2008.

My one-upping started after this fellow rubbed his Core i7-920 in my Core 2 Quad Q9550's face. Game on! But really, I didn't have the funds or the knowledge to beat that.

Then a good friend Bayley showed up at MIT, and things got serious reasonably fast. In particular, my upgrade path looked something like this:
  • Core 2 Quad Q9550 4-core/8GiB DDR2
  • Some Intel Xeon W35xx 4-core/24GiB DDR3
  • 2x Intel Xeon X5650 6-core/24GiB DDR3
  • 4x AMD Opteron 6164 HE 12-core/128GiB DDR3 ECC
Then Bayley and I both realized that we had to switch to rackable computers for any sort of ease in managing hardware. I took a break from single-image systems and built half a blade server:
  • 2x Intel Xeon L5320 4-core/8GiB DDR2 FB-DIMM
While Bayley got a Sun Box®:
  • 8x AMD Opteron ??? 4-core/128GiB DDR2 ECC
In a valiant attempt to dethrone me, he patched the Sun's BIOS with the microcode for hex-core CPUs, but the computer only recognized one core of one processor of the eight that he put it. Much wow.

My AMD box cemented 1st place in sheer awesomeness for student-owned computers for a little over a year, until Bayley discovered mainframes on eBay:
  • Some IBM thing with 16x Intel Xeon E75xx 6-core/256GiB DDR2 ECC
Mind you, I have cemented awesomeness density, since my AMD box fits perfectly in 1U, while Bayley's monstrosity needs 16U, and a whole lot more power. :-) Not to mention that it blew a circuit breaker while trying to install Ubuntu…

Leave it to me, my worst enemy, to dethrone myself. I wanted to repackage the AMD box into a legitimate 1U chassis that I found on eBay for not too much money, since it had sat on a piece of cardboard (for insulation!) atop the dorm dresser. After the computer happily booted in the chassis, I jiggled one of the unscrewed heatsinks and shorted the motherboard. A nice spark flew from a voltage regulator to the copper heatsink and poof!

gg no re Bayley

*

There's also a GPU story, which I shall not neglect. I went to MIT with my trusty aforementioned 8800GTS 320MB. A few swapfests later, Bayley wound up with a quartet of GTX 460s. It was mainly used for benchmarking Holy Balls, a demanding multi GPU raytracer, and got really toasty after a while. Good old Fermi.

The cryptocurrency scene started getting traction with the advent of profitable scrypt-coin mining. AMD cards were far superior in hashes/watt and competent in hashes/sec. Bayley got his hands on a few AMD 7850s, the preferred mining card, among other cards. I went extra long and got 11 cards from various sources (newegg, eBay, etc) since retailers caught on to the mining demand. Luckily I was able to dump my cards at cost (after eBay commission) after Mt. Gox blew and before everyone else wanted to dump their cards. Bayley kept mining, and even upgraded to 7950s as well as a 6990 when prices decreased and good deals appeared.

But wait, I'm back! I had the privilege of acquiring a new Mac Pro (affectionately known as the "trash can") with dual AMD D700 graphics cards. For all intents and purposes, they are two workstation grade cards (think neutered W9000s), each with 6GiB VRAM. So I can confidently say that I retake the GPU crown.

*

Meanwhile, with the abundance of swapfests at MIT, Bayley acquired multiple storage nodes for not too much money (and the networking infrastructure to back the system). To top that, he accidentally won half an SGI Altix and soon to be the glorious 1TiB of RAM on eBay.

*

GiB and TiB stand for Gibibytes and Tebibytes, because I'm anal and care about these distinctions.