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Comment: Re:What happened to C#? (Score 1) 100

by thestuckmud (#46667589) Attached to: Microsoft To Allow Code Contributions To F#

F# and C# are both multi-paradigm languages, and are both built on top of the CLR type system. Functional style is more natural in F#, but C# has first class functions (and lambda), too. F# has loops and assignment, but nothing as powerful/abuse-inviting as the C-style for loop. Neither approach is the one true style.

If you believe the proverb, "library design is language design" [from Bell Labs? Was it Stroustrup?], then F# is a much different language from other ML variants as it has native access to Dot Net/Mono libraries.

Comment: Re: Isn't a drone the same as an R/C airplane? (Score 2) 136

by thestuckmud (#46183163) Attached to: These Are the Companies the FAA Has Sent notices To For Using Drones

According to this, the difference in the US is that recreational model aircraft are covered by FAA Advisory Circular (AC) 91-57, while Unmanned Aerial Systems require either a Certificate of Waiver or Authorization (COA) or Special Airworthiness Certificate in the Experimental Category (SAC-EC). Operation in restricted airspace is another matter. In all cases, a pilot in command must maintain control of the aircraft (which I take to mean line of sight is required).

The other agency US unmanned aerial systems (UAS) have to contend with is the FCC. There are frequencies available for recreational RC use, and amateur radio bands, but last time I checked there was nothing for controlling a commercial UAS.

+ - How to Get Help Online (2013 Edition) 5

Submitted by Shlomi Fish
Shlomi Fish (3362) writes "The document How to Get Help Online (2013), aimed at inexperienced and not too net-savvy people, aims to summarise and spread the knowledge, of where and how to get help with one’s problems (especially technical and software-related ones). While many Slashdot visitors will not gain many new insights from it, it may be useful for them to recommend less experienced people to read it. Furthermore, its Creative Commons licence (the CC-by-nc) allows others to reuse it and build upon it. And comments and suggestions for improvements are welcome."

Comment: Re: Video editing... (Score 1) 501

by thestuckmud (#45778753) Attached to: A Flood of Fawning Reviews For Apple's Latest

I'm just going by reviews that use superlatives like "insanely quiet". Apple claims an impressive 12bDA at idle, which is going to be hard to hear even with the unit on top of a desk, but it is easy to turn the fans off at idle. I am assuming that the unique thermal design is really being exploited to minimize fan noise.

I disagree that about the competition being "very quiet". Quiet in a relative way, sure, but not as quiet as I would like. For reference, consider the recent Xeon powered HP workstation (non-liquid-cooled) under my desk for reference. It is actually quite nice compared to the screaming hair dryer fans of old, but, under load, the whooshing of air through it is plainly audible even with a gas fireplace fan blasting away 2m from my ears. Turning off the HP under these circumstances gives me a sense of relief from its noise. Compare that with this description: "during an Apple demo, a high-end Mac Pro, complete with upgraded processor and graphics cards, was live-rendering multiple 4K videos, and we couldn’t hear the fan over the normal room noises."

Comment: Re:Expensive Garbage Can ? (Score 1) 501

by thestuckmud (#45777625) Attached to: A Flood of Fawning Reviews For Apple's Latest

I guess if ... you don't know about hard drive failure rates, then it could be an attractive choice.

What hard drive? These come with SSDs.

Personally I don't like anything about it except for the dual-gpu support.

By all means choose a computer with the features you want. For my part, I think I've finally found a serious computer without distracting fan noise.

Comment: Re:Assembly == SLOW ; JAVA == FAST! (Score 2) 372

If your C is faster than your Assembly, that's because your Assembly is crap.

You are kidding yourself if you think you can write programs in assembler that run faster than the equivalent in C. Look at what my compiler generates for the C statement "return x/372;" with 64 bit ints on x64:

movslq %edi, %rax
imulq $738919105, %rax, %rax
movq %rax, %rcx
shrq $63, %rcx
sarq $38, %rax
addl %ecx, %eax
popq %rbp
ret

Your only practical approach as a human writing this in assembler is to use the slower 64 bit divide instruction. Puzzling out optimizations like this is a job much better suited for a the code generator in a compiler.

This is just one example among many arithmetic tricks of the trade. Register allocation and loop unrolling are two more low level optimizations that are no fun. At least not for me. I'd rather write the program in C, profile it, optimize my algorithms, and only then consider rewriting inner loops in assembler. Actually, I'd rather write the program in a proper modern programming language, and speed up its inner loops by rewriting them in C/assembler.

Comment: Air Drag? Really??? (Score 1) 137

by thestuckmud (#44395955) Attached to: The Physics of the World's Fastest Man

The paper assumes "that in the 100 m sprint he is able to develop a constant horizontal force F0 during the whole race", fits an air drag formula to laser measurements of an actual race, and concludes that Bolt expends 81.58kJ of mechanical work during a 100m sprint lasting 9.58 seconds. That may sound OK on the face of it, but 81.58kJ/9.58s is about 8500W (11.5HP) - more than four times the 2000W instantaneous maximum power output of elite track sprint cyclists. OK, maybe you believe in the overwhelming superiority of runners over cyclists. In that case, consider the drag of a body traveling at sprinting speeds. According to this bicycle power calculator, a non-aerodynamic rider might use as much as 500W at the maximum speed attained by Bolt. It is simply not possible that a runner's drag would be 17 times greater than an upright cyclist with knobby tires. This seems to prove that the paper's main assumption is wrong.

So what is going on? Well, we can see that there is an incredibly good fit between experimental data and the model. Clearly a combination of linear and quadratic force terms make the equation fit. However, the obvious answer is that these terms must primarily influence the force the sprinter is able to exert as a function of velocity. As I said, I'm not much of a runner, but I distinctly recall running out of leg speed when I used to attempt to sprint. Bolt's advantage seems to have more to do with muscle speed than raw power.

The failure to discuss this glaring discrepancy suggests the paper should not have been accepted for publication in its current form.

Comment: Re:One problem (Score 1) 353

by thestuckmud (#44233453) Attached to: Volkswagen Concept Car Averages 262 MPG
I think you misunderstand the engineering behind these tires. Much of the improved performance in wet conditions and lower rolling resistance can be chalked up to their higher air pressure. Contact area is approximately vehicle (corner) weight divided by air pressure, so these tires will have smaller contact area than conventional tires. The larger diameter allows the tire to deform less to achieve that contact patch, further reducing rolling resistance. And a narrower tire has less air resistance.

Comment: Re:thing of the past (Score 1) 120

I think that charging of batteries is mostly limited by the plug that it's connected to.

Charge time is often limited by battery chemistry and construction. Lithium ion batteries, for example, are typically limited to a rate of 1C (a theoretical 1 hour charge time from empty to 100%). In practice, those li-ion batteries take several hours to reach 100% charge because the rate slows down dramatically near as the battery reaches full.

Consider the Tesla S sedan: Not coincidentally, Tesla's 300A Supercharger stations "can charge about half the battery in 30 minutes." We are not likely to see faster charging options until new battery technology becomes available. Of course "the plug" (or more likely the socket in this case) substantially limits charging rate: Tesla's 1.4kW wall socket charger provides a mere 5 miles of range per hour of charge.

Luck, that's when preparation and opportunity meet. -- P.E. Trudeau

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