6 ms·

The Comdyna GP-6 analogue computer that I use daily at work

64 points by pmarin 8y ago

stillworks 8y ago
How fascinating. I wonder what is the measure of precision on such computers for real numbers. And can this be used for integer math if at all ?
- brandmeyer 8y ago
  Closest that I've come is working with opamp circuits. Generally speaking: Doing almost anything in analog is more expensive than doing it digitally. These days, the only things you do in analog are things that are impossible to do digitally, like anti-aliasing filters. RF is another story, but even there the economics are changing with direct-sampling ADCs. 1% resistors are easy to find. 0.1% can be found at a high price. 0.01% can also be found, for roughly 1 USD/ea, and only on the E12 sequence. Capacitors are worse by a factor of 5 or so. Those tolerances turn into scale-factor error, common-mode rejection ratio, DC bias, and so on. Without breaking the bank, you can easily build a circuit to maybe 7 bits of accuracy, and for a small timer you can do maybe 12 bits or so. But in volume, its almost always better economically to use a lower-accuracy circuit and perform calibration at the factory or in the field. Aside: I fact-checked myself on Digikey and was pleasantly surprised to find that you can get 0.01% resistors without "calling for quote." A few years ago the limit for small-timers was effectively only about 0.1%. Even still 1 USD/ea is a BOM budget-buster for all but the most narrow of uses.
  - esmi 8y ago
    Circuit with an ENOB > 12 definitely exist. See table 1 in the app note below for an example. https://www.maximintegrated.com/en/app-notes/index.mvp/id/5384 https://www.maximintegrated.com/en/app-notes/index.mvp/id/53...
    - brandmeyer 8y ago
      ADC's well above ENOB exist. 24-bit sigma-delta ADC's are pretty easy to come by without breaking the budget. But analog computation circuits (subtraction, gain, addition) are another matter entirely.
      - esmi 8y ago
        Doesn’t one make a sigma delta from subtracting, integration and gain stages? If one could make a sigma delta one could make other stuff too. https://en.m.wikipedia.org/wiki/Delta-sigma_modulation#/media/File%3ABlock_Diagram_Delta-Sigma_ADC(minor_change).svg https://en.m.wikipedia.org/wiki/Delta-sigma_modulation#/medi...
        brandmeyer 8y ago
        Sigma-delta ADC's are built in such a way that component errors result in changes in bandwidth instead of changes in scale factor.
- deleted 8y ago
  [deleted]
djhworld 8y ago
I appreciate the OP (of the reddit post) wants to keep his/her identity secret but I remain completely unsatisfied with the response to someone asking exactly what they need this analogue computer for > My job is to make and maintain models of economic trends in my company’s industry. I find analogue computing to be the best way for me to easily and effectively model dynamic real world systems. I don't have much of an understanding of analgoue computers so I can't grasp why this computer is better at solving this sort of problem over a digital one.
- pgeorgi 8y ago
  > so I can't grasp why this computer is better at solving this sort of problem over a digital one As the original author mentioned in the discussion, it's better for _them_ and that's enough in that situation to keep doing it that way. The assessment may be entirely different for you, or maybe even everybody but that author.
  - lodi 8y ago
    It hasn't been established that it's better, only that he or she thinks it's better--and we're all trying to understand why that is. Because we're (or at least I am) 99.99% sure that it's much, much worse. To start with, the whole thing could easily be simulated in software...
    - dfox 8y ago
      I suspect that the main reason why it is better is UX of representing whatever you want to calculate by physical structure and tunable parameters by physical knobs.
- leggomylibro 8y ago
  I don't have a good answer, but there does appear to be a history of using analog computing for financial modeling. One famous example is the MONIAC, which used fluids to simulate the flow of money: https://en.wikipedia.org/wiki/MONIAC https://en.wikipedia.org/wiki/MONIAC I wonder if 'fuzzy' or uncertain models like economic ones can tolerate or benefit from slightly less deterministic algorithms.
jonfw 8y ago
This thread had a very good OP. I don't buy that this is at all useful though. It would be trivial in a modern computer to get much more precision than this. I feel like his arguments about conversion from analog to binary would have merit, if the scale that modern computers operated at wasn't so severe. Yeah conversion from analog to binary can be lossy, but the losses become smaller as you use more memory. And these days we have access to a lot of memory. What's interesting is that our modern computational platforms have capabilities that far exceed most of our use cases. And this is a good demonstration of why.
- halfeatenpie 8y ago
  From what I've gathered and read from OP's comments, it sounds like their analog model makes sense and is precise enough for them to work with. People talk about how much more powerful a "32-core Xeon machine" is and they're not wrong, but just because new technology is available you also have to look at is it worth it to transition over/update it. I have an example from my daily work. We were hired to update a company's model from 6 years ago. Their model is an Excel VBA model that we're rebuilding in Python with an increase resolution of detail and accuracy. However, for our "more accurate" model to be accepted, we have to also prove the following: - We have to show that our model's outputs are the same as the VBA's model for the same input/starting condition (makes sense at a higher level, but at a higher resolution this means you have to spend more time looking at why a specific value is in a specific way and can be different from the lower resolution model) - Train the new users on the new model (knowledge transfer) - Ability to update and modify the new model wherever they need to change it or understand it - Understand the limitations and the constraints of the new model This basically boils down to how much time is needed in training the new model, how much money and time is needed to invest in building a new model, and is it really worth it to build a new model when the old model has worked good enough for now (and you understand the limitations of said model and is within your needs)? There's only so much time in the day and you obviously have a ton of other tasks that also needs your attention, and getting these newer models verified and accepted by the board is great but it's also additional meetings and time that you need to setup with them and get everything OK-ed... doubly hard when everyone else is also super busy. I'd say modern computational platforms are better when it comes to raw power, but the logic and just resources required to build, verify, accept, and train (human resources-wise) the new model might just not be fully worth it. Remember, there are also other industries other than tech that uses computer hardware to get jobs done.
madengr 8y ago
That's a fascinating read. Analog computing may make a comeback: https://spectrum.ieee.org/computing/hardware/not-your-fathers-analog-computer https://spectrum.ieee.org/computing/hardware/not-your-father...
driverdan 8y ago
To me OP comes off as a curmudgeon that won't learn how to do this more efficiently in software. There's no reason why they couldn't do it faster and more accurately in software.
- gh02t 8y ago
  I kinda feel the same, but I'd probably put a bit more of a charitable spin on it. I can certainly see how it might be more intuitive to the OP to use an analog computer and how it might not be worth the cost of moving to a software system when this is good enough. What I would disagree with is any assertion that this is objectively the best way, and OP does acknowledge in the original thread that this isn't necessarily the overall optimal setup.
basementcat 8y ago
Analog computers aren’t all that unusual. For example, many airplane pilots use a Jepperson Circular computer to calculate headings and other parameters. https://www.amazon.com/Jeppesen-Circular-Computer-diameter-JS514237/dp/B003VSCID0 https://www.amazon.com/Jeppesen-Circular-Computer-diameter-J... Even Spock used it on the Enterprise. https://www.flickr.com/photos/10901121@N06/1196208122 https://www.flickr.com/photos/10901121@N06/1196208122
- Koshkin 8y ago
  Well, a slide rule (even a circular one) is not an "analog computer"...
  - howard941 8y ago
    How about the E6B's wind vector calculating elements? Those pieces are on the reverse side of the slide rule bits. https://en.wikipedia.org/wiki/E6B https://en.wikipedia.org/wiki/E6B
    - zackbloom 8y ago
      Still no, an analog computer is an electronic computer which uses varying voltages and currents to calculate results. It's not the same as a manual computer.
      - Someone 8y ago
        Analog computers need not be electronic. They can be mechanical (e.g. https://en.wikipedia.org/wiki/Digi-Comp_I https://en.wikipedia.org/wiki/Digi-Comp_I) or hydraulic (e.g. https://en.wikipedia.org/wiki/MONIAC https://en.wikipedia.org/wiki/MONIAC), too. (Generic entry point: https://en.wikipedia.org/wiki/Analog_computer https://en.wikipedia.org/wiki/Analog_computer)
rotexo 8y ago
As some of the commenters on this reddit thread mentioned, any electronic musician who has a Eurorack rig containing, for instance, a Make Noise Maths, technically uses an analog computer regularly at work.

64 points by pmarin 8y ago

How fascinating. I wonder what is the measure of precision on such computers for real numbers. And can this be used for integer math if at all ?

brandmeyer 8y ago
Closest that I've come is working with opamp circuits. Generally speaking: Doing almost anything in analog is more expensive than doing it digitally. These days, the only things you do in analog are things that are impossible to do digitally, like anti-aliasing filters. RF is another story, but even there the economics are changing with direct-sampling ADCs. 1% resistors are easy to find. 0.1% can be found at a high price. 0.01% can also be found, for roughly 1 USD/ea, and only on the E12 sequence. Capacitors are worse by a factor of 5 or so. Those tolerances turn into scale-factor error, common-mode rejection ratio, DC bias, and so on. Without breaking the bank, you can easily build a circuit to maybe 7 bits of accuracy, and for a small timer you can do maybe 12 bits or so. But in volume, its almost always better economically to use a lower-accuracy circuit and perform calibration at the factory or in the field. Aside: I fact-checked myself on Digikey and was pleasantly surprised to find that you can get 0.01% resistors without "calling for quote." A few years ago the limit for small-timers was effectively only about 0.1%. Even still 1 USD/ea is a BOM budget-buster for all but the most narrow of uses.
- esmi 8y ago
  Circuit with an ENOB > 12 definitely exist. See table 1 in the app note below for an example. https://www.maximintegrated.com/en/app-notes/index.mvp/id/5384 https://www.maximintegrated.com/en/app-notes/index.mvp/id/53...
  - brandmeyer 8y ago
    ADC's well above ENOB exist. 24-bit sigma-delta ADC's are pretty easy to come by without breaking the budget. But analog computation circuits (subtraction, gain, addition) are another matter entirely.
    - esmi 8y ago
      Doesn’t one make a sigma delta from subtracting, integration and gain stages? If one could make a sigma delta one could make other stuff too. https://en.m.wikipedia.org/wiki/Delta-sigma_modulation#/media/File%3ABlock_Diagram_Delta-Sigma_ADC(minor_change).svg https://en.m.wikipedia.org/wiki/Delta-sigma_modulation#/medi...
      - brandmeyer 8y ago
        Sigma-delta ADC's are built in such a way that component errors result in changes in bandwidth instead of changes in scale factor.
deleted 8y ago
[deleted]

djhworld 8y ago

I appreciate the OP (of the reddit post) wants to keep his/her identity secret but I remain completely unsatisfied with the response to someone asking exactly what they need this analogue computer for > My job is to make and maintain models of economic trends in my company’s industry. I find analogue computing to be the best way for me to easily and effectively model dynamic real world systems. I don't have much of an understanding of analgoue computers so I can't grasp why this computer is better at solving this sort of problem over a digital one.

pgeorgi 8y ago
> so I can't grasp why this computer is better at solving this sort of problem over a digital one As the original author mentioned in the discussion, it's better for _them_ and that's enough in that situation to keep doing it that way. The assessment may be entirely different for you, or maybe even everybody but that author.
- lodi 8y ago
  It hasn't been established that it's better, only that he or she thinks it's better--and we're all trying to understand why that is. Because we're (or at least I am) 99.99% sure that it's much, much worse. To start with, the whole thing could easily be simulated in software...
  - dfox 8y ago
    I suspect that the main reason why it is better is UX of representing whatever you want to calculate by physical structure and tunable parameters by physical knobs.
leggomylibro 8y ago
I don't have a good answer, but there does appear to be a history of using analog computing for financial modeling. One famous example is the MONIAC, which used fluids to simulate the flow of money: https://en.wikipedia.org/wiki/MONIAC https://en.wikipedia.org/wiki/MONIAC I wonder if 'fuzzy' or uncertain models like economic ones can tolerate or benefit from slightly less deterministic algorithms.

jonfw 8y ago

This thread had a very good OP. I don't buy that this is at all useful though. It would be trivial in a modern computer to get much more precision than this. I feel like his arguments about conversion from analog to binary would have merit, if the scale that modern computers operated at wasn't so severe. Yeah conversion from analog to binary can be lossy, but the losses become smaller as you use more memory. And these days we have access to a lot of memory. What's interesting is that our modern computational platforms have capabilities that far exceed most of our use cases. And this is a good demonstration of why.

halfeatenpie 8y ago
From what I've gathered and read from OP's comments, it sounds like their analog model makes sense and is precise enough for them to work with. People talk about how much more powerful a "32-core Xeon machine" is and they're not wrong, but just because new technology is available you also have to look at is it worth it to transition over/update it. I have an example from my daily work. We were hired to update a company's model from 6 years ago. Their model is an Excel VBA model that we're rebuilding in Python with an increase resolution of detail and accuracy. However, for our "more accurate" model to be accepted, we have to also prove the following: - We have to show that our model's outputs are the same as the VBA's model for the same input/starting condition (makes sense at a higher level, but at a higher resolution this means you have to spend more time looking at why a specific value is in a specific way and can be different from the lower resolution model) - Train the new users on the new model (knowledge transfer) - Ability to update and modify the new model wherever they need to change it or understand it - Understand the limitations and the constraints of the new model This basically boils down to how much time is needed in training the new model, how much money and time is needed to invest in building a new model, and is it really worth it to build a new model when the old model has worked good enough for now (and you understand the limitations of said model and is within your needs)? There's only so much time in the day and you obviously have a ton of other tasks that also needs your attention, and getting these newer models verified and accepted by the board is great but it's also additional meetings and time that you need to setup with them and get everything OK-ed... doubly hard when everyone else is also super busy. I'd say modern computational platforms are better when it comes to raw power, but the logic and just resources required to build, verify, accept, and train (human resources-wise) the new model might just not be fully worth it. Remember, there are also other industries other than tech that uses computer hardware to get jobs done.

madengr 8y ago

That's a fascinating read. Analog computing may make a comeback: https://spectrum.ieee.org/computing/hardware/not-your-fathers-analog-computer https://spectrum.ieee.org/computing/hardware/not-your-father...

driverdan 8y ago

To me OP comes off as a curmudgeon that won't learn how to do this more efficiently in software. There's no reason why they couldn't do it faster and more accurately in software.

gh02t 8y ago
I kinda feel the same, but I'd probably put a bit more of a charitable spin on it. I can certainly see how it might be more intuitive to the OP to use an analog computer and how it might not be worth the cost of moving to a software system when this is good enough. What I would disagree with is any assertion that this is objectively the best way, and OP does acknowledge in the original thread that this isn't necessarily the overall optimal setup.

basementcat 8y ago

Analog computers aren’t all that unusual. For example, many airplane pilots use a Jepperson Circular computer to calculate headings and other parameters. https://www.amazon.com/Jeppesen-Circular-Computer-diameter-JS514237/dp/B003VSCID0 https://www.amazon.com/Jeppesen-Circular-Computer-diameter-J... Even Spock used it on the Enterprise. https://www.flickr.com/photos/10901121@N06/1196208122 https://www.flickr.com/photos/10901121@N06/1196208122

Koshkin 8y ago
Well, a slide rule (even a circular one) is not an "analog computer"...
- howard941 8y ago
  How about the E6B's wind vector calculating elements? Those pieces are on the reverse side of the slide rule bits. https://en.wikipedia.org/wiki/E6B https://en.wikipedia.org/wiki/E6B
  - zackbloom 8y ago
    Still no, an analog computer is an electronic computer which uses varying voltages and currents to calculate results. It's not the same as a manual computer.
    - Someone 8y ago
      Analog computers need not be electronic. They can be mechanical (e.g. https://en.wikipedia.org/wiki/Digi-Comp_I https://en.wikipedia.org/wiki/Digi-Comp_I) or hydraulic (e.g. https://en.wikipedia.org/wiki/MONIAC https://en.wikipedia.org/wiki/MONIAC), too. (Generic entry point: https://en.wikipedia.org/wiki/Analog_computer https://en.wikipedia.org/wiki/Analog_computer)

rotexo 8y ago

As some of the commenters on this reddit thread mentioned, any electronic musician who has a Eurorack rig containing, for instance, a Make Noise Maths, technically uses an analog computer regularly at work.