Analog Computers

https://blog.degruyter.com/algorithms-suck-analog-computers-future/

by StreamBright • 9 years ago

166 102 9 years ago

blog.degruyter.com

The author certainly has a point, but I wonder if analog computers (in the sense of DA/AD + ICs that can be plugged into general purpose systems) suffer from economies of scale? Maybe energy + depreciation costs of general purpose computers are still lower than ordering a minimum of 10~100k units of some custom analog computer w/ good enough quality control.

Apparently something similar to FPGA exists for analog signals [1], I wonder how popular/practical it is.

[1] https://books.google.com.br/books?id=qjnnBwAAQBAJ&pg=PA93&lp...

anfractuosity• 9 years ago

I got some FPAA chips I assume you're referring to, the ones I've got are Anadigm ones, I need to get round to using them. The downside is the ones I've got, simply make use of switched capacitors for creation of filters, so there will be some form of discretization in the temporal domain I guess.

kitotik2• 9 years ago

Excellent. So maybe all that time I’ve wasted playing with analogue modular synthesis will finally pay off!(?)

nixpulvis• 9 years ago

My thoughts exactly. beep boop

dphov• 9 years ago

Stop comparing brain with computer

mindcrime4• 9 years ago

If any of you guys are into analog computing, just as an FYI, there's a sub-reddit dedicated to the topic (full disclosure, I started this particular one). analogcomputing.reddit.com

There's not a ton of content there yet, but please feel free to add anything you come across. I'm a fan of the idea and suspect, like the author of this piece, that there is "something there".

smellf• 9 years ago

How long have subreddits been accessible through a subdomain? Is this something the subreddit mods have to turn on?

snuxoll• 9 years ago

It's been this way since I started using the site in 2009.

mindcrime4• 9 years ago

For as long as I can remember and I've been using Reddit since about 2008.

xfer2• 9 years ago

The author's so called analog computers can be built by using FPGAs. And the term he might be reaching for is called data-flow programming.

mindcrime4• 9 years ago

The author's so called analog computers

Why do you say "so-called"?

can be built by using FPGAs.

Also, FPAA's (Field Programmable Analog Array)[1]

[1] https://en.wikipedia.org/wiki/Field-programmable_analog_arra...

xfer2• 9 years ago

Maybe it was the wrong term. My point was we have them and they are used, but they are not cost efficient in general. So saying that they will be the future of computing, is a bit ridiculous imo.

crispyambulance2• 9 years ago

Yeah I remember reading the chatter about FPAA's back in the 90's.

It seemed like an exciting idea, but it never took off perhaps because the kind of accuracy that makes it worthwhile was not achievable?

Miky2• 9 years ago

Not really. FPGAs are fundamentally digital and pretty much give you a bunch of logic gates to work with ("Field-Programmable Gate Array"). The author's proposed architecture would instead provide an array of components that perform analog operations, such as summing, multiplication, and integration or differentiation, over analog voltages.

robotresearcher2• 9 years ago

FPGAs are fundamentally analog, depending on if 'fundamental' means what was in the designer's head or what you actually fabricated. You are thinking about them and using them as if they were digital.

Adrian Thompson at Sussex University used a genetic algorithm to auto-design FPGA circuits in the early 90s. Since no one told the GA that FPGAs were supposed to be logic circuits, it happily used the FPGA as an analog machine.

Even an Intel i7 chip is an analog machine that approximately implements the i7 computer design. They throw away the ones that don't approximate it up to tolerance.

danmaz74• 9 years ago

Instead, you program it by changing the interconnection between its many computing elements – kind of like a brain

This is one of the worst "brain" analogies I've read lately.

aj72• 9 years ago

The brain is not an analog computer.

chroem-• 9 years ago

Well it's definitely not a Turing machine.

smitherfield3• 9 years ago

It is however definitely Turing-complete.

carapace• 9 years ago

But it can imagine a turing machine (well enough to write software for same.)

I think the meme of the Universal Machine is causing some sort of phase transition in humanity as it propagates.

aj72• 9 years ago

It would be interesting to simulate that airflow in LTSpice, given that that analog contraption can do it.

ramgorur2• 9 years ago

It's strange that the article does not mention anything about hydraulic macroeconomics and MONIAC, they were once widely used to verify theories in economics.

https://en.wikipedia.org/wiki/MONIAC https://en.wikipedia.org/wiki/Hydraulic_macroeconomics

valarauca1• 9 years ago

It's too bad MONIAC couldn't model the Stagflation of the 70's or it might be a useful model.

alimw• 9 years ago

So this looks interesting, but my first thought is how can a conserved quantity like water model something like money that is created and destroyed?

kybernetikos2• 9 years ago

I don't think there's any requirement that the amount of water in the model remains constant. In principle you could drain or open valves to add more.

cr0sh• 9 years ago

A good summary of analog computers can be found on the wikipedia article:

https://en.wikipedia.org/wiki/Analog_computer

Takeaway: Analog computers are limited in precision and by "analog noise"; the precision of the components used determine the precision of the output. Usually no more than 3 or 4 decimal places are possible, at least with the tech that was used in their heydey. I would say that is still close to the case even today. Of course, one could do things like cryogenic cooling or such, but it becomes a cost factor at that point.

Something else that wasn't mentioned:

The ADALINE/MADALINE memister technology is an analog component, and is a hardware component equivalent to a McCulloch–Pitts neuron model (perceptron).

The memister is NOT to be confused with the memristor, which is a different technology; the memister was a 3-terminal device (memory transistor):

https://en.wikipedia.org/wiki/ADALINE

...whereas a memristor is a two terminal device ("memory resistor"):

https://en.wikipedia.org/wiki/Memristor

robotresearcher2• 9 years ago

Usually no more than 3 or 4 decimal places are possible

By that do you mean accurate to 1 part in 100 (3dp) or 1000 (4dp) or what? Since the scale of a representation is arbitrary, I'm not sure what dp means here.

flavio812• 9 years ago

Good question. I guess precision is finally going to be fractions of the max voltage swing allowed by the computer. For example, if voltage goes from -5 to +5 volts, the voltage swing is 10v, and if noise allows 0.1mV of precision, then the precision is 1/100000 of the full voltage swing.

This could be expressed, at the end, simply in decibels, though. Signal-to-noise, as in classic analog systems.

JKCalhoun5• 9 years ago

Kind of seems like if you are measuring the analog computers virility by the number of decimal places it can represent maybe you are mis-using the machine. I mean how many decimal places can you or I do in our head in real-time?

jim-jim-jim• 9 years ago

While that may be true, those 3-4 decimal places are really _warm_

wfunction2• 9 years ago

I seem to recall there were clever but well-known techniques in analog to get higher accuracy than that of your actual components, through negative feedback IIRC. So why is it correct to say that the precision of the components is what limits output precision? Wouldn't the technique potentially make a difference? (and yeah I know accuracy != precision but I'm using them loosely... the distinction doesn't seem relevant here)

gugagore• 9 years ago

I haven't thought it through, but feedback lets you do a few (perhaps connected?) things: 1. explore a trade-off between gain and bandwidth, 2. Reject disturbances and nonlinearities.

So you could have a high gain but "low precision" (in the sense of deviating from an ideal, not in the sense of not being noisy) component, and through feedback you can make a low gain, high precision (having desired properties, not low noise) component.

RachelF2• 9 years ago

Analog (or analogue) computers have their uses, however, in my experience, with analogue electronic computers, they have many problems:

- limited dynamic range of perhaps 30dB (1000)

- it is easy to saturate a signal (there is no overflow bit)

- oscillations are easy to induce, but once again hard to detect, especially in a circuit in the middle of a calculation chain

- noise gets amplified across the system

JKCalhoun5• 9 years ago

Reminded me of A.K. Dewdney's "Computer Recreations" column in "Scientific American" back in the day (I think a lot of people may have hated on his column since it followed in the shadow of Martin Gardener's infamous "Mathematical Recreations"). One of the "analog computers" he mentioned was using dried spaghetti to sort numbers — where the length of each spaghetti noodle represented the magnitude of a number. Of course grabbing them into a bundle in your hand and setting the bundle on end on a flat surface would "sort" the values.

Would the surface tension across a film that accurately finds the shortest path between n points be considered a "computation"?

One thing fascinating by "analog computers" is the way they seem to be practically instantaneous regardless of n. That is perhaps part of the efficiency reflected in the article.

pjc504• 9 years ago

The high point of analogue computing for control systems may have been Concorde. It normally operated in fly-by-wire through an analogue interconnection: the so-called synchro/resolver system, which is a AC servo control system. The flight computers (mostly but not entirely analogue) provided autothrottle and autostabilisation.

("Somewhere" in the Concorde megathread is a description of its analogue computers: http://www.pprune.org/tech-log/423988-concorde-question.html )

adamnemecek5• 9 years ago

I'm hoping that analog computing will come back in the form of photonic analog computing. This would be more powerful than quantum digital computing (you know the things that people are wasting time on).

Fun fact, with analog computing, one could imagine achieving Real Computation (https://en.wikipedia.org/wiki/Real_computation) which is above and beyond Turing. completeness.

Note the fun sentence "If real computation were physically realizable, one could use it to solve NP-complete problems, and even #P-complete problems, in polynomial time. ".

We are on a wrong evolutionary branch of computing. Bits are lame-o-rama, whereas differentiable signals are pure unadulterated flavortown.

mgraczyk• 9 years ago

What you're describing is generally accepted to be physically unrealizable. In fact, the sentence that follows your quoted sentence cites two commonly known physical limitations that prevent the existence of your "computational class above and beyond Turing".

Whether or not there exist physically realizable computations that are not computable by a turing machine is an open question, but most physicists and computational complexity theorists seem to believe there does not exist such a class.

https://en.wikipedia.org/wiki/Church%E2%80%93Turing_thesis

adamnemecek5• 9 years ago

Read unlimited as arbitrary precision.

I'm familiar with the Turing thesis but he's wrong.

ramgorur2• 9 years ago

"computational class above and beyond Turing"

what does it mean?

11thEarlOfMar2• 9 years ago

So, Keith Emerson's Moog Synthesizer[0] was an analog computer, yes?

[0] http://i.telegraph.co.uk/multimedia/archive/03593/emerson6_3...

kitotik2• 9 years ago

Certainly. Most modular synths have all the basics - Sum, divide, multiply, add, XOR, etc.

And don’t forget, analogue random is the shit. In your face entropy!

crispyambulance2• 9 years ago

It sure is. As are all analog modular synths. Its just that the "problems" worked on by such analog computers are ...different.

funkdobiest• 9 years ago

I was going to speak on this as the pictures look just like my Eurorack. The module I have called Maths does all the arithmetic functions needed.

11thEarlOfMar2• 9 years ago

Cool, I had to come back and post this link of a block diagram of the Moog:

http://cdm.link/app/uploads/2016/03/dangeroussynth.jpg

janekm• 9 years ago

Analog computing makes a lot of sense in the context of genetic algorithms and "deep learning" and I wouldn't be surprised if there's already some ASICs under design using those principles. One big challenge is that the design kits from the foundries aren't likely to include all the analog computer cells that would be needed (but perhaps for example a current mirror into a MIM capacitor could make for an integrator?).

shmageggy2• 9 years ago

Genetic algos are inherently discrete, so I can't see analog computing being all that useful for them.

orbifold• 9 years ago

You can look into neuromorphic computing, there are several projects that use digital-analog hybrid systems to implement neural networks.

read_only• 9 years ago

At the ISCA conference last week, Yoshua Bengio, of DNN fame, talked about their early efforts in analog computing. Here are some related slides of his: http://www.iro.umontreal.ca/~bengioy/talks/Brains+Bits-NIPS2...

brian-armstrong• 9 years ago

A related topic - running digital logic at subthreshold voltages, where transitions usually (but not always) happen correctly. It can be useful if you're attempting to measure something probabilistically anyway

https://pdfs.semanticscholar.org/7244/1c8377b1dfde1909d21463...

trophycase• 9 years ago

First I've heard of analog computers but it sounds super interesting. So basically the structure of the system defined the algorithm and is therefore very specialized and efficient?

jayd16• 9 years ago

Something that might be interesting is some kind of analog fpga for neural networks. Seems like NN weighting would translate well.

smitherfield3• 9 years ago

The human brain is a great example – its processing power is estimated at about 38 petaflops, about two-fifths of that of TaihuLight.

Huh? So we now have computers more powerful than the human brain? I thought that was still some decades off. And how would one even measure such a thing? In the apples-to-apples comparison, a stupid human trick floating-point calculation savant might manage 1 flop/s.

oldandtired• 9 years ago

In speed yes, in terms of continuous parallel computing power at low energy levels, technology hasn't come even close. In terms of sensory input and processing, not even close.

I find it amusing that there is much hype about computer systems beating humans in very specialised areas, such as go and chess.

But the missing piece here is that the human is still doing this while continuously processing all the sensory input that is occurring to that human, dealing with so much more than what the computer system is dealing with. The computer system is dealing with one and only one subject matter at a speed many magnitudes faster and is only just getting ahead.

dom02• 9 years ago

one and only one subject matter at a speed many magnitudes faster and is only just getting ahead.

Kasparov didn't simulate 200 million moves per second to make his move.

nitwit005• 9 years ago

If you see an estimation of human brain computation power, it's probably best to assume it's nonsense. There are wildly different estimates, and as computers have gotten faster, the estimates seem to have risen, which suggests ego is involved.

mikeash2• 9 years ago

I recall checking a few years ago, and it would have taken about 40,000 high-end GPUs to match the common estimates of the computing power of the brain. It's no doubt much lower now.

The problem is that it takes far more than raw computing power to make AI. We have sufficient computing power but we don't know how to use it, not even close.

As for how it's measured, it's basically a matter of guesstimating the computing power of a single neuron based on its inputs, outputs, and the computation it appears to do to map between them, and then multiplying by the number of neurons in the brain. This is horribly imprecise so estimates vary a lot (describing it as "38" gives the estimate way too much credit, should probably say 10 or 100 instead) but they're probably in the very rough ballpark.

supermdguy• 9 years ago

What causes this difference? First of all, the brain is a specialized computer, so to speak, while systems like TaihuLight and TSUBAME3.0 are much more general-purpose machines, capable of tackling a wide variety of problems.

That's why digital computers have so far been so much more successful than analog computers. While analog computers may have the potential to be "better", they'd require massive global hardware and software changes to become the next big thing. People are lazy, and there's no way they'd want to port everything over to a completely different paradigm just for better energy efficiency and speed.

gautam1168• 9 years ago

this feels like forcibly renaming electronics engineering as programming

peterburkimsher2• 9 years ago

My boss at my previous job at Fisher & Paykel Healthcare in New Zealand is using analogue computing today.

He developed Pertecs, which is a rudimentary analog computer paradigm written in C.

http://tcode.auckland.ac.nz/~mark/Signal%20Processing%3A%20P...

He got me to write some code to compile schematic diagrams into the XML config files. He's also done something similar now to compile from LaTeX, and he ported the controller from a Mac Mini to a Raspberry Pi.

Pertecs is being used to control an artificial lung, which is used for research into obstructive sleep apnoea (snoring).

The problem is, he's retiring, and I'm probably the only other person in the world who knows how to use his program. I would move back there, but the immigration policy got more difficult (minimum salary of $75k), so I'm seriously wondering whether I should stay in Taiwan longer and try to naturalise here.

sleet• 9 years ago

I believe the $75k minimum salary is for non-skilled jobs (the point being, if you're in a non-skilled but 'high' paying role we're still interested in you). The minimum salary for skilled jobs is $50k [1][2]

That and I doubt you would find many people working at F&P Healthcare that earn less than $75k.

[1] https://www.immigration.govt.nz/about-us/media-centre/news-n... [2] https://www.immigration.govt.nz/employ-migrants/hire-a-candi...

peterburkimsher2• 9 years ago

"we're" - it sounds like you're connected to NZ immigration! I can fill you in with more details if you're interested.

$75k is 4x my current salary in Taiwan. Yes, I know the economy is totally different in NZ, but I don't have high hopes that changing country will suddenly make me become rich. My boss here pays me the minimum that the government allows for a Masters graduate on a foreigner work visa.

The other consideration is my girlfriend. She applied for Working Holiday, but wasn't one of the 600 lucky ones. We were in an internet café with the fastest connection in Kaohsiung, but the site just wouldn't load in time. She's 30, so she can't try again next year. If we wanted to get a partnership visa, we would have to live together and share a bank account for 1 year. Getting married doesn't even help, just living arrangements.

We're getting kind of sidetracked from the original topic of analog computers, but if it's something you want to talk about more, then just search for my name on Facebook and send me a message. It would be nice to personify the immigration forms.

cctan• 9 years ago

At last, we will have a truly random number generator! Not the simulated fake rand() using timestamps as seed.

RachelF2• 9 years ago

Most modern Intel and AMD CPUs have a truly random number generator, generated in a non-digital way.

ChuckMcM2• 9 years ago

I have fond memories of building an analog computer as a project from Popular Electronics that simulated a lunar lander mission. At reset you had fuel, altitude, horizontal and vertical velocity. Your input was an angle and a thrust knob (two potentiometers) and a comparative that latched when altitude reached 0 based on your velocities being less than 1m/s. It was tremendous fun to play but no graphics, just some mA meters to tell you your status.

JKCalhoun5• 9 years ago

Sounded cool, so searched for it. Page 41:

http://www.americanradiohistory.com/Archive-Elementary-Elect...

ChuckMcM2• 9 years ago

Great! That is definitely the thing I built so other than wrong magazine name and it went up instead of down, it's exactly like I remember it :-)

ankurdhama• 9 years ago

In analog computers there are no algorithms, no loops, nothing as they know it. Instead there are a couple of basic, yet powerful computing elements that have to be interconnected cleverly in order to set up an electronic analog of some mathematically described problem.

This is exactly why the digital computer has won over the analog computer.

dom02• 9 years ago

Uhm, no. Analogue vs. digital computers use fundamentally different kinds of computation. Analogue computers were not used for "programming", nor was it really necessary for the simulations done on them.

Essentially, with an analogue computer you have a rack full of analogue building blocks and you build an electronic system equivalent to your real-world system from them. Then you can apply inputs and observe outputs. Often, the inputs were connected to sensors in a device, and the outputs were connected to actuators or recorders.

When analogue computers were already in wide use, there were maybe three digital computers on the whole planet. Later still, in the 60s to perhaps the early 80s "analogue computers" could (to varying degrees) perform some simulations orders of magnitude faster than contemporary digital computers. Only when digital computers became fast, cheap and easy enough to do these they became a replacement, however, moving from an analogue computer to a digital program could be quite difficult, since the two operate in vastly different ways.

Large systems often used digital computers since the ~70s for e.g. recording and analyzing outputs: a company in my home town developed test rigs for performance and crash testing of cars (and also did the testing to some extent); they still had a massive hybrid computer in the 80s (multiple analogue racks plus I think two DG Nova systems).

dragontamer• 9 years ago

Luckily, with today’s electronic technology it is possible to build integrated circuits containing not only the basic computing elements but also a crossbar that can be programmed from an attached digital computer, thus eliminating the rat’s nest of wires altogether.

This is the most important paragraph in the entire article.

Analog Computers can be made very small. It'd take an ASIC, but the 741 OpAmp was less than 100 transistors. A more modern OpAmp might be under 1000 transistors... although noise issues would be abound.

Bernd Ulmann has developed a methodology that performs non-trivial computations (such as: http://analogparadigm.com/downloads/alpaca_4.pdf), but its still hand-programmed by connecting wires together.

If it were digitally programmed with a digital crossbar switch (consisting of CMOS Analog Gates instead), then it'd be controllable by a real computer.

I think what Ulmann is arguing here... is to use analog computers as a "differential equation accelerator". Perform a lot of computations in the digital world, but if you need to simulate a differential equation, then simulate it on an analog circuit instead.

And there are a large number of interesting mathematical problems that are described as differential equations.

-----------------

The main issues, as far as I can see, would be the multiplier, logarithm, and exponential functions. IIRC, these are created using a bipolar transistor... and modern manufacturing doesn't really mix BJT with MOSFET.

I mean, IGBT transistors exist, but modern computers are basically MOSFET all the way down. MOSFETs would be able to make a lot of things though: digital potentiometers / variable resistors... the crossbar switch, capacitors, resistors, and OpAmps.

And all of those can simulate addition, subtraction, derivatives and integrals. More than enough to build a "differential equation accelerator" that the author proposes.

Analog Computers

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