# Introduction to polyDB

The polyDB extension provides access to the polyDB database. It comes bundled with polymake, so there is no need to install extra software, except for the MongoDB.pm perl package. If you encounter any errors or problems concerning polyDB, please don't hesitate to ask in the forum.

The database is hosted on the polymake server (at db.polymake.org, where you also find a web interface). The objects are arranged in collections which reside in so-called databases. See here for a list of available databases and collections.

From the polymake shell the function db_info prints information about available databases and collections.

polytope > db_info();
DATABASE: LatticePolytopes
This database contains various classes of lattice polytopes.

Collection: SmoothReflexive
All smooth reflexive lattice polytopes in dimensions up to 8 up to lattice equivalence. The lists were computed with the algorithm of Mikkel Oebro (see [[http://arxiv.org/abs/0704.0049|arxiv: 0704.0049]]) and are taken from the [[http://polymake.org/polytopes/paffenholz/www/fano.html|website of Andreas Paffenholz]].

In dimensions up to 7 the database contains the properties:
H_STAR_VECTOR, REFLEXIVE, CONE_DIM, date, _id, LATTICE_CODEGREE, N_INTERIOR_LATTICE_POINTS, SMOOTH, N_LATTICE_POINTS, FACET_WIDTHS, VERTICES, FACETS, CENTROID, N_VERTICES, contributor, LATTICE_DEGREE, LATTICE_VOLUME, EHRHART_POLYNOMIAL_COEFF, N_BOUNDARY_LATTICE_POINTS, ESSENTIALLY_GENERIC, VERY_AMPLE, F_VECTOR, GORENSTEIN, FEASIBLE, LINEALITY_SPACE, AFFINE_HULL.

In dimension 8 it only contains the minimal set:
LINEALITY_SPACE, CONE_DIM, date, _id, VERTICES, FEASIBLE, N_VERTICES, contributor.

__________________

DATABASE: Tropical
This database contains tropical objects.

Collection: TOM
All known non-realisable tropical oriented matroids with parameters n=6, d=3 or n=d=4. They were computed using polymake with the tropmat extension and Topcom. You need the extension [[http://solros.de/polymake/tropmat|tropmat]] for this.

__________________

Note that this command only lists those databases for which you have read access. The command takes the options db to list only collections in a particular database, collection to list only one collection (in this case db must also be given), and username, if you have access to some collections not (yet) publicly available.

It is also possible to host your own database on your server. This is, however, not yet documented.

In this tutorial we are going to use the collection SmoothReflexive in the database LatticePolytopes, which contains all smooth reflexive lattice polytopes in dimensions up to 8.

### Queries

Database queries are given as perl hashes. In its most basic form a query has the form

 { "PROPERTY1" => <value1>, "PROPERTY2" => <value2>, ... }

for example

 { "DIM" => 3, "N_VERTICES" => 7 }

Note that the database is pretty strict with types, so strings always need to be quoted, while integers must not be. The following would fail:

 { "DIM" => "3" }

The empty query is allowed:

 {}

returns all objects of a collection. You can query elements in an array with their index, e.g.

 { "F_VECTOR.1" => 12 }

gives polytopes with 12 edges (the entry at position one of the f-vector).

For more sophisticated querying see the section on advanced queries.

#### db_query

Note that you should not use this function if you expect a large number of objects to match your search criteria. (Check this with db_count.) In this case create a DatabaseCursor instead, as explained here.

The function db_query expects a query, and as options a database and a collection name. The following code returns an Array<LatticePolytope> of all 3-dimensional polytopes in our collection of smooth reflexive lattice polytopes.

polytope > $a = db_query({"DIM" => 3}, db=>"LatticePolytopes", collection=>"SmoothReflexive"); Note that (depending on server capacity and network speed) this may take a while. Sometimes it might even result in a time out. In this case just try again (and feel free to contact us if the problem persists). Check the section on custom variables to omit having to enter db and collection on every query. Now we can browse through the elements of $a and inspect their properties, e.g.:

polytope > print $a->[0]->SMOOTH; 1 polytope > print$a->[0]->REFLEXIVE;
1
polytope > print $a->[0]->VERTICES; 1 1 1 0 1 1 0 0 1 0 1 -1 1 1 -2 1 1 1 1 1 1 0 1 1 1 0 -3 1 1 -4 1 -3 polytope > print$a->size;
18

#### List queryable entries

You can print a list of all queryable entries of a database collection:

polytope > db_print_searchable_fields(db=>"LatticePolytopes",collection=>"SmoothReflexive");
Entries for smooth reflexive polytopes in dimensions 1 to 7
----------------------------
AFFINE_HULL  [dense, int]
CENTROID
CONE_AMBIENT_DIM  [int]
CONE_DIM  [int]
EHRHART_POLYNOMIAL_COEFF
FACETS  [dense, int]
FACET_WIDTHS  [int]
(...)

Entries for smooth reflexive polytopes in dimension 8
----------------------------
(...)

Entries for smooth reflexive polytopes in dimension 9
----------------------------
(...)

#### Request a limited number of objects

You can use the limit option:

polytope > $a=db_query({'DIM' => 7}, db=>"LatticePolytopes", collection=>"SmoothReflexive", limit => 10); polytope > print$a->size;
10

#### Request possible values of a property

You can use the option distinct, e.g.

$a=db_query({'DIM' => 3}, distinct=>"N_VERTICES"); returns an array that contains all values N_VERTICES can take for a 3-dimensional polytope. #### Request only one representative of a collection You can use the db_query function with the option representative if you are only looking for one arbitrary example matching certain query criteria, e.g.: polytope >$p = db_query({"CONE_DIM"=>4, "N_VERTICES"=>10}, representative=>1);

polytope > print $p->_id; F.3D.0002 polytope > print$p->DIM;
3
polytope > print $p->N_VERTICES; 10  Note that you might get a different polytope (with another _id) if you repeat the above code. You can also use this function to extract a polytope with a certain _id: polytope >$p = db_query({"_id"=>"F.4D.0123"});

#### Custom variables

If you are going to access the same collection all the time, you can set the custom variables $db_name and $collection_name:

$PolyDB::default::db_name = "LatticePolytopes";$PolyDB::default::collection_name = "SmoothReflexive";

These variables are used as default for the database and collection name if you omit the options of db_query and db_count, e.g.:

$a = db_query({"CONE_DIM"=>5, "N_VERTICES"=>15}); If you do set_custom$PolyDB::default::db_name = "LatticePolytopes";
F.3D.0001
polytope > db_print_metadata($a->[1]); collection: SmoothReflexive contributor: Andreas Paffenholz creation_date: 2016-08-30 database: LatticePolytopes id: F.7D.000001 tag: object version: 3.0 ### poly_db_count The function poly_db_count returns the number of objects matching your query criteria, e.g.: polytope > print db_count({"DIM"=>3}); 18 polytope > print db_count({"DIM"=>4}); 124 polytope > print db_count({"DIM"=>5}); 866 polytope > print db_count({"DIM"=>6}); 7622 polytope > print db_count({"DIM"=>7}); 72256 polytope > print db_count({"DIM"=>8}); 749892 ### db_ids There is another function db_ids that is very similar to db_query but only returns an array of IDs, e.g.: polytope > print db_ids({'CONE_DIM' => 8}, db=>"LatticePolytopes", collection=>"SmoothReflexive", limit => 10); F.7D.009999 F.7D.000000 F.7D.000001 F.7D.000002 F.7D.000003 F.7D.000004 F.7D.000005 F.7D.000006 F.7D.000007 F.7D.000008 ### Advanced queries You can use the full query syntax of MongoDB, as explained here. #### Ranges Instead of specifying the exact value of a property we might be interested in specifying ranges for numerical properties. The following queries the polytopes with (strictly) less than 100 vertices: polytope > print db_count({"N_VERTICES" => { '$lt' => 100 }});
107917

You can also query those with less than 100 but (strictly) more than 50 vertices:

polytope > print db_count({"N_VERTICES" => { '$lt' => 100, '$gt' => 50 }});
97595

The operators $lte (for less than or equal) and $gte (for greater than or equal) are also supported.

You can also use regular expressions to search for strings. Since there are not so many string-valued properties around, let's try with the _id. The following is another way to count 4-dimensional polytopes (those with _id beginning with F.4D).

polytope > print db_count({"_id" => qr/F.4D/});
124

We could also count those objects added in August 2013:

polytope > print db_count({"date" => qr/2013-08-/});
80886  

If you expect your query to match a large number of objects (which you can find out using db_count on your query), you should construct a database cursor instead of using the function db_query. A PolyDB cursor accepts the same arguments as a normal db_query, i.e. you can specify database and collections, you can narow the search with a query, and you can set limit and skip. The options representative and distinct don't work here. The request for a PolyDB cursor returns a pointer into the database, and each call to next retrieves another object. For large result sets, this saves memory locally and reduces the time until you can start with computations. Note though that you have to create a new cursor if you want to start from the beginning.

  $c = db_cursor({"DIM"=>4}, db=>"LatticePolytopes", collection=>"SmoothReflexive"); A cursor has four special methods: • next: retrieves the next object from the database • has_next: Checks if there are still objects that satisfy the query in the database that have not yet been retrieved. • at_end: similar to has_next, returns true if no further object can be retrieved. • count: tells you the number of results that match your query  polytope > print$c->count;
124
polytope > while ($c->has_next) { print$c->next->N_VERTICES." "; }
11 8 17 13 15 18 15 16 12 12 15 16 16 12 16 16 16 13 12 12 9 21 17 17 23 30 13 17 15 18 16 15 12 17 21 21 18 24 18 17 16 13 13 12 15 12 9 20 24 20 16 16 20 20 24 20 24 20 20 16 20 24 20 21 20 24 24 20 20 16 16 16 16 12 25 30 36 20 24 20 16 16 16 20 16 12 17 16 16 16 16 20 16 12 15 18 15 20 24 18 15 15 16 11 11 12 12 12 13 16 16 12 12 12 8 8 12 9 16 12 8 8 9 5

### Sorting, etc.

If you want the objects to be retrieved in a certain order, the optional parameter sort_by allows to specify a sorting order, using 1 for ascending and -1 for descending. E.g. assume you want to sort ascending by _id

polytope > $c = db_cursor({"DIM"=>4}, db=>"LatticePolytopes", collection=>"SmoothReflexive", sort_by=>{'_id'=>1}); polytope > for ($i=1; $i<=10; ++$i) { print $c->next->name." "; } F.4D.0000 F.4D.0001 F.4D.0002 F.4D.0003 F.4D.0004 F.4D.0005 F.4D.0006 F.4D.0007 F.4D.0008 F.4D.0009 … or descending by number of vertices: polytope >$c = db_cursor({"DIM"=>4}, db=>"LatticePolytopes", collection=>"SmoothReflexive", sort_by=>{'N_VERTICES'=>-1});

polytope > while($c->has_next){print$c->next->N_VERTICES." ";}
36 30 30 25 24 24 24 24 24 24 24 24 24 23 21 21 21 21 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 18 18 18 18 18 18 17 17 17 17 17 17 17 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 15 15 15 15 15 15 15 15 15 15 13 13 13 13 13 13 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 11 11 11 9 9 9 9 8 8 8 8 8 5

If you want to skip the first few objects, you can do so by specifying skip:

polytope > $c = db_cursor({"DIM"=>4}, db=>"LatticePolytopes", collection=>"SmoothReflexive", sort_by=>{'_id'=>1}, skip=>100); polytope > for ($i=1; $i<=10; ++$i) { print \$c->next->name." "; }
F.4D.0100 F.4D.0101 F.4D.0102 F.4D.0103 F.4D.0104 F.4D.0105 F.4D.0106 F.4D.0107 F.4D.0108 F.4D.0109
• user_guide/howto/poly_db_tutorial.txt