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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

#41

Post by d--b »

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 really need a way to set which cells are fixed and which cells are allowed to move if you want to move past basic examples.

Most times you know what you want to do. like => if the user modifies that cell, find a solution for those specific ones.

If you can enter that info, then you have a lot more constrains for your solver and will avoid a lot of edge cases where everything goes to 0, and you can check that the calculation entered is indeed reversible or not, or if it could have multiple solutions, and so on.

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

#43

Post by nico »

Suppafly wrote: post #40
jamestimmins wrote: post #38

Earlier quoted context omitted.

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.

Lots of people working in different fields end up reinventing things that have been known to math for centuries, often in clunky roundabout ways. I imagine some of them figure out things not known to math, but it's far more likely to go the other way.

> Lots of people working in different fields end up reinventing things that have been known to math for centuries

I remember reading, about a year or two ago, about a medical doctor that published a paper rediscovering calculus (I just looked it up, it happened in 1994, there’s been many articles and videos about it)

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

#45

Post by alexchantavy »

nico wrote: post #43
Suppafly wrote: post #40

Earlier quoted context omitted.

Lots of people working in different fields end up reinventing things that have been known to math for centuries, often in clunky roundabout ways. I imagine some of them figure out things not known to math, but it's far more likely to go the other way.

> Lots of people working in different fields end up reinventing things that have been known to math for centuries I remember reading, about a year or two ago, about a medical doctor that published a paper rediscovering calculus (I just looked it up, it happened in 1994, there’s been many articles and videos about it)

lmao: https://en.wikipedia.org/wiki/Tai%27s_model

This is such a great story

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

#46

Post by RachelF »

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.

A lot of the time engineers are focussed with solving a problem, to build a working machine/program, while academics just want to publish.

This is also true with patents.

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

#48

Post by aatd86 »

maplethorpe wrote: post #34
aatd86 wrote: post #14

LOL! Gemini suggested to implement this to me literally yesterday: bidirectional computations. The example was that given a temperature in Celsius and Fahrenheit, modifying either of them should update their counterpart. In angular that would be two linked signals for instance, but even that is a bit fringe. Gemini was going for something even more elaborated. I told Gemini that spreadsheets were actually not doing t…

That's weird, Gemini told me not to do this.

To not do what, to not implement a constraint solver for bidirectional formulas? If you input my above comment it is for sure going to weigh the pros and cons. https://gemini.google.com/share/f40bf53d9c21

Excerpt from the initial convo with gemini: Thinking with 3 Pro December 11, 2025 at 09:59 PM

2. Propagators (Constraint Networks)The Problem: Your valueref binder and watch logic handle one-way data flow well. But complex forms (e.g., "Start Date must be before End Date," or "Fahrenheit Celsius") require messy, cyclic event handlers to keep everything in sync.The Academic Concept: Propagators (Alexey Radul / Gerald Sussman, MIT).Instead of functions ($A \rightarrow B$), you define Constraints. A network of constraints seeks a consistent value for all connected nodes. It is "multi-directional" by design.

I see my message above being downvoted, I don't even know why ;D

In the end Gemini did agree that it was not necessary to introduce this level of complexity for my use case.

To be fair, Victor goes further because he adds a solver on top. In the research of a solution that might make sense. The issue in general is that not everything has a reverse operation so, in a sense, it is but an approximation.

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

#49

Post by uoaei »

adonovan wrote: post #39

“Formulas that update backwards” is the main idea behind neural networks such as LLMs: the computation network produces a value, the error in this value is computed, and then the error quantity is pushed backward through the network; this relies on the differentiability of the function computed at each node in the network.

All those words and you forget to provide people the breadcrumbs to learn more for themselves.

The term of interest is "backpropagation".

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

#50

Post by Towaway69 »

Suppafly wrote: post #40
jamestimmins wrote: post #38

Earlier quoted context omitted.

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.

Lots of people working in different fields end up reinventing things that have been known to math for centuries, often in clunky roundabout ways. I imagine some of them figure out things not known to math, but it's far more likely to go the other way.

Folks shouldn’t be afraid to “rediscover” stuff.

Primarily because the learnings you make are the same as the original “discoverer”. Without those learnings, you might not be able to arrive at your true destination.

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