Move radius, diameter and eccentricity methods from generic_graph.py to graph.py and digraph.py

[vipul79321]

Currently radius, diameter and eccentricity computation methods are in generic_graph.py file. Since graph and digraph both have different algorithms for their computation. So it would be nice to have these method separately for graph and digraph in respective files.

CC: @dcoudert

Component: graph theory

Keywords: gsoc20

Author: Vipul Gupta

Branch/Commit: 9e2dcc8

Reviewer: David Coudert

Issue created by migration from https://trac.sagemath.org/ticket/29660

[vipul79321]

Branch: u/gh-vipul79321/ticket29660

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

bf852a4

radius, diameter, eccentricity, center, periphery moved to graph and digraph separately

[sagetrac-git]

Commit: bf852a4

[vipul79321]

Author: Vipul Gupta

[dcoudert]

comment:4

• There is no need to add before the methods

+    # Eccentricity
+    # Radius

• This part is a perfect example of why we must add an eccentricity method in boost backend. It makes no sense to use boost to compute APSP, then return a dictionary of dictionaries with the distances (taking very long time to build and consuming a lot of memory) and finally get the largest value. We could directly return the eccentricities from boost.

+            if algorithm in ['Floyd-Warshall-Python', 'Floyd-Warshall-Cython', 'Johnson_Boost']:
+                dist_dict = self.shortest_path_all_pairs(by_weight, algorithm,
+                                                         weight_function,
+                                                         check_weight)[0]
+                algorithm = 'From_Dictionary'

Overall, I think this change ease the identification of missing methods and bad implementation choices. We must avoid as much as possible the use of dist_dict.

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

9e2dcc8

unneccessary comments removed

[sagetrac-git]

Changed commit from bf852a4 to 9e2dcc8

[vipul79321]

comment:6

Replying to @dcoudert:

• There is no need to add before the methods

+    # Eccentricity
+    # Radius

Done

[dcoudert]

Reviewer: David Coudert

[dcoudert]

comment:7

LGTM.

[dcoudert]

Changed keywords from gsoc to gsoc20

[dcoudert]

comment:8

just update the keyword to gsoc20

[vbraun]

Changed branch from u/gh-vipul79321/ticket29660 to 9e2dcc8