This Movable Feast Machine demo is based on a previous one.
Three programmable agents are used to build and maintain a 2-layer membrane.
The main idea is to move most of hardcoded behavior to program trees and universal "physical laws" (in this demo -- attraction/repulsion between atoms).
Hardcoded parts are building program trees (TreeBuilder element) and setting initial conditions for the demo.
YouTube videos:
- setting up, bootstrapping, starting to build: video 1;
- completing the membrane: video 2
- starting multiple cells with
DemoMultipleelement: video 3
On Ubuntu, intstall ulam package (it contains both ULAM and MFM) from PPA, see ULAM Tutorial.
Or install ULAM and MFM from source: http://robust.cs.unm.edu/doku.php?id=dev:install_ulam. Note that for develop branch, Makefile.local.mk should use $ULAM_ROOT_DIR instead of $ROOT_DIR.
After that, running make in repo directory will compile *.ulam source files and run the result in MFM.
Place a single Demo (white De) atom to start the demo. To start with multiple cells place DemoMultiple (white DM) atom.
Demo element builds a program loop from Package atoms containing program data and attaches a TreeBuilder to beginning of "bootstrap" program. It also creates DemoInitialMembraneBuilder that in turn builds the first layer of the membrane around the program loop.
Program trees and data sequences are both built from Package atoms, packages in a tree have exec flag set in their data. Trees are built from sequences by TreeBuilder and executed by Exec. After a tree is complete, TreeBuilder attaches Exec atom to the tree and deletes itself.
All programs are stored in program loop. Each program sequence starts with a Package atom that has a 1-byte tag value assigned and can be marked as active or inactive (these are marked with a green or red diagonal line in the picture above). The first program is used to build other ones, bootstrapping the whole thing: the agent crawls along the loop, attaches TreeBuilders to active tagged atoms and then deactivates them. The idea was that it can later receive a signal with a tag value to re-activate tagged Packages and build more copies, but this is not used in the demo. Other programs are used to build, maintain and grow the membrane.
Attaching membrane atoms for 2nd layer:
Repairing the membrane using attached atoms:
The last program randomly inserts atoms in the membrane, the other two then attach 2nd layer atom to it and fix the bonds, growing the membrane.
If the membrane is damaged (by manually removing an atom from either layer) it is usually repaired successfully, although sometimes the agents can interfere with each other's work.
Listing of all the programs used in the demo: Demo.ulam:137.
More details on how program tree is executed: Exec.ulam:6.
Atoms can attract and repulse each other, also the bonds don't like to be stretched to full length (see ForceUtils.ulam). When a new site is selected for a diffusable atom, first all the forces acting on the atom are summed up and possible sites are weighed by how similar their positions are to the resulting vector (see QDiffusableT.ulam:45). Exact values and calculations are not very important, just seem to be good enough for the demo.
Membrane atoms repulse other Membrane atoms and Packages. This allows the membrane to keep the contents inside and prevents it from collapsing.