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Show HN: I made a spreadsheet where formulas also update backwards

victorpoughon.github.io

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Re: Show HN: I made a spreadsheet where formulas also update backwards

#81

Post by areyousure »

I have wanted one general application of this idea in a spreadsheet. Specifically, I track some of my running, including speed (pace), distance, and time. Under different circumstances, I have exactly two of the three available and I want the third to be computed, but it varies which. I have found it fairly difficult to implement this kind of data entry in Google Spreadsheets and Excel, even know conceptually it's a very simple constraint "a*b=c" where I know some two variables.

As a more substantive comment: You may find the thesis "Propagation networks : a flexible and expressive substrate for computation" by Alexey Radul interesting. https://dspace.mit.edu/handle/1721.1/54635

Re: Show HN: I made a spreadsheet where formulas also update backwards

#83

Post by RobotToaster »

jamestimmins wrote: post #38
spiderice wrote: post #35

Earlier quoted context omitted.

A random tool like this would be the most entertaining possible way for something like that to be unleashed on the world

My brother once suggested that there are probably bits of code/algorithms that would be world changing if they were released in academic journals, but instead were written by some unknowing programmer in an afternoon for their job coding embedded systems for refrigerators. This particular example may be unlikely, but it's a very fun idea.

An anonymous 4chan user once solved a 25 year old maths problem, to answer a question about the watch order of an anime. https://www.scientificamerican.com/article/the-surprisingly-...

Re: Show HN: I made a spreadsheet where formulas also update backwards

#84

Post by amelius »

d--b wrote: post #41

The examples are great and these bidirectional calculators are something that people would love to have in traditional spreadsheets. So much so that Credit Suisse, which basically was running everything on heavily modded Excel, created a full language whose outputs were Excel spreadsheets capable of doing that. That thing called “paradise” was a total monstrosity but showed how much people wanted this. That said, you…

> and these bidirectional calculators are something that people would love to have in traditional spreadsheets

People want them in general programming languages too. I can't count the number of times I had to implement the same function multiple times, but backwards in various ways.

Re: Show HN: I made a spreadsheet where formulas also update backwards

#85

Post by amelius »

nico wrote: post #44

Could you build an inverse kinematics solver with this? (I recently watched a youtube video of someone iteratively working out the solutions for a robotic arm, by alternating modifying the inputs and the results)

Closed form solutions might be more efficient (in time, energy) and perhaps more numerically stable.

Re: Show HN: I made a spreadsheet where formulas also update backwards

#87

Post by sroerick »

fouronnes3 wrote: post #62
spiderice wrote: post #35

Earlier quoted context omitted.

A random tool like this would be the most entertaining possible way for something like that to be unleashed on the world

Jokes aside, let's say someone does figure out how to break RSA over a weekend project. The evil options are easy to come up with, but what is the actually responsible, ethical, thing to do? Never tell anyone?

Pretend you had developed a quantum computing advancement and push people to post quantum encryption

Re: Show HN: I made a spreadsheet where formulas also update backwards

#88

Post by jsax »

This is pretty cool.

This functionality is called ‘break back’ in a lot of enterprise modelling software. See [IBM TM1](https://www.ibm.com/docs/en/cognos-planning/10.2.1?topic=bre...) and [Anaplan](https://help.anaplan.com/breakback-1b7aa87d-aa13-49f6-8f7d-d...). They generally work in terms of scaling the inputs to match the new output though, which is a bit more basic than this approach.

Re: Show HN: I made a spreadsheet where formulas also update backwards

#90

Post by fouronnes3 »

jsax wrote: post #88

This is pretty cool. This functionality is called ‘break back’ in a lot of enterprise modelling software. See [IBM TM1]( https://www.ibm.com/docs/en/cognos-planning/10.2.1?topic=bre... ) and [Anaplan]( https://help.anaplan.com/breakback-1b7aa87d-aa13-49f6-8f7d-d... ). They generally work in terms of scaling the inputs to match the new output though, which is a bit more basic than this approach.

Interesting, thanks! I had never heard of this. Yes, bidicalc is much more advanced. You can update any value of an arbitrary dependency graph of cells.
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