orientation of the graph in the web interface about proofofconcept

[bhpayne]

this is related to #70

[bhpayne]

added a "linear index" float value to each step within a derivation; this could be leveraged for orientation in d3js

[bhpayne]

In graphviz, pin node that has the lowest "linear index" to the top of the graph. If necessary, pin the highest "linear index" to the bottom of the graph.

https://stackoverflow.com/questions/8309201/graphviz-fixed-node-positions

https://graphviz.gitlab.io/_pages/doc/info/attrs.html#d:pin

https://observablehq.com/@magjac/placing-graphviz-nodes-in-fixed-positions

[bhpayne]

Example derivations where this is relevant:

• Euler equation proof

[bhpayne]

In a large graph I added a single pos to one node

1337934 [shape=invtrapezium, color=blue, label="",image="/home/appuser/app/static/declareinitialexpr.png",labelloc=b, pos="0,0!"];

and then ran

neato -Tpng graphviz.dot -o newgraph.png

That didn't work, probably because neato wasn't looking for positions. I also tried an explicit pin,

1337934 [shape=invtrapezium, color=blue, label="",image="/home/appuser/app/static/declareinitialexpr.png",labelloc=b, pos="0,0!", pin=true];

but that didn't alter the layout. When I told neato to look for positions, I get an error because only one has pos

neato -n -Tpng graphviz.dot -o newgraph.png
    Error: node 5427510 in graph physicsDerivation has no position as required by the -n flag

Then I added pos="0,0" to all the other nodes. The neato -n worked but the graph was unreadable (and the one static 0,0! didn't seem to take effect).

[bhpayne]

I can get node positions to change if I use non-negative coordinate values, e.g., pos="2,1!", pin=true

I pinned the first and last inference rules but the layout was not improved

[bhpayne]

https://github.com/allofphysicsgraph/proofofconcept/tree/gh-pages/v7_pickle_web_interface/flask/from_freelancers/20200608_pinned_nodes_Evgeniy

3f5b75b