Stock-flow diagrams with signed links

[tim-at-topos]

Enriching the theory of stock-flow diagrams to have positive and negative links, instead of merely links. Includes a mass-action simulation analysis.

[tim-at-topos]

@epatters I'm trying to get + and - to appear on positive / negative links in the visualisation, and it's proving very frustrating. What's currently confusing me even more is the file svg_styles.module.css, which seems to tell me that links should be blue and rectangles should be a delightful ube colour, but this isn't what's happening in reality. Any suggestions?

[epatters]

Thanks Tim, this looks great so far!

My only major request is that we create a new theory in the frontend rather than replacing the old one. There are at least three reasons for this:

1. It won't break any existing models that use the old theory
2. More importantly, it's consistent with our philosophy of having a family of languages of increasing expressiveness and complexity, with migrations between them, like we've done with CLDs. (As we've discussed, the UX for these migrations currently isn't great, but that's a separate problem.)
3. More importantly still, in my perusal of stock-flow diagrams in the wild, the links very often don't have signs, and thus keeping the old theory around is a way of respecting the tradition while still being able to go beyond it

[epatters]

@epatters I'm trying to get + and - to appear on positive / negative links in the visualisation, and it's proving very frustrating. What's currently confusing me even more is the file svg_styles.module.css, which seems to tell me that links should be blue and rectangles should be a delightful ube colour, but this isn't what's happening in reality. Any suggestions?

Argh, there appears to be a regression on next in

• coloring places in a Petri net
• coloring links in a stock-flow diagram on next.

On prod they look fine. @kasbah, I wonder if this is an unintended consequence of #888? I don't have time to investigate right now.

But note @tim-at-topos that the fun ube color is specific to places in Petri nets: the CSS selector is .place rect. However, making the links be blue should work and, until recently, did.

[kasbah]

On prod they look fine. @kasbah, I wonder if this is an unintended consequence of #888? I don't have time to investigate right now.

My observations differ. Importantly I don't see any regression from prod to next.

• Petri net place borders are colored everywhere (prod, next, loaclhost/main)
• Petri net fill is set to transparent on localhost but colored on main

screenshots

There is a conflict between .node rect { fill: transparent; } set in visualization/graph_svg.css and fill: #e6e6ff set in svg_styles.module.css. Presumably development and production servers result in different resolution order.

• Stock and flow links are not colored anywhere (prod, next, localhost/main)

EDIT: This is also due to a similar conflict. It can be worked around with !important.

I made an issue for it: #913

[epatters]

Presumably development and production servers result in different resolution order.

That must be it, although I do see different behavior in prod and next/local for Petri nets. In any case, I've got a fix in #915.

[epatters]

This is looking good! @tim-at-topos, I made a few small cleanups (see new commits).

I've also rebased off main, which includes my fixes to the CSS for SVG graph visualizations (#915). However, instead of delaying further, I'm going to merge this as-is and let you follow up with a PR to add the positive/negative signs to the stock-flow visualization. Thanks!