Bands (#62)

* Added one file to bands

* Protect snappy doctests with +SNAPPY

* Added core code of bands

* bands: added code for searching for ribbon discs/concordances

* Link.linking_matrix does not require Sage

* links.bands: add regression test

* Fix snappy import issue

* links.bands: add user methods to Link

* ribbon_concordant_links: add RibbonLink accelerator

* Require snappy_manifolds>=1.3

* Fix typos in comments

* DTcodec.link: Standardize crossing labels

Author: NathanDunfield

setup.py

@@ -206,15 +206,15 @@ def run(self):
 install_requires = ['decorator',
                     'networkx',
                     'packaging',
-                    'snappy_manifolds>=1.1.2',
+                    'snappy_manifolds>=1.3',
                     'knot_floer_homology>=1.2.2']
 
 setup( name = 'spherogram',
        version = version,
        install_requires = install_requires,
        python_requires = '>=3',
        dependency_links = [],
-       packages = ['spherogram', 'spherogram.links',
+       packages = ['spherogram', 'spherogram.links', 'spherogram.links.bands',
                    'spherogram.links.test', 'spherogram.codecs',
                    'spherogram.dev', 'spherogram.dev.dev_jennet'],
        package_dir = {'spherogram' : 'spherogram_src', 'spherogram.dev':'dev'},

spherogram_src/codecs/DT.py

@@ -949,6 +949,9 @@ def link(self):
         link._build_components(component_starts)
         if not link.is_planar():
             raise ValueError('DT code does not seem to define a *planar* diagram')
+        # Give the crossings standard names
+        for i, C in enumerate(link.crossings):
+            C.label = i
         return link
 
     def KLPProjection(self):

spherogram_src/links/__init__.py

@@ -5,6 +5,7 @@
 from .tangles import Tangle, CapTangle, CupTangle, RationalTangle, ZeroTangle, InfinityTangle, MinusOneTangle, OneTangle, IntegerTangle, IdentityBraid, ComponentTangle, join_strands
 from . import orthogonal
 from .random_links import random_link
+from . import bands
 
 Link.view = orthogonal.orthogonal_draw
 
@@ -25,4 +26,4 @@ def pdf_docs():
            'Tangle', 'CapTangle', 'CupTangle', 'RationalTangle',
            'ZeroTangle', 'InfinityTangle', 'MinusOneTangle', 'OneTangle', 'IntegerTangle',
            'IdentityBraid', 'join_strands',
-           'pdf_docs', 'random_link']
+           'pdf_docs', 'random_link', 'bands']

spherogram_src/links/bands/__init__.py

@@ -0,0 +1,19 @@
+"""
+
+Submodule for doing band moves to construct ribbon concordances and
+search for ribbon disks.  Code originally developed by Nathan Dunfield
+and Sherry Gong for their paper::
+
+  Ribbon concordances and slice obstructions: experiments and examples
+  https://arXiv.org/abs/FILLIN
+
+"""
+
+from . import merge_links
+from . import core
+from . import search
+from .core import Band, normalize_crossing_labels
+from .search import verify_ribbon_to_unknot
+
+
+