1. Graphs, Continued
ECE 297

2. Review: Map as a Graph Intersections  Nodes Street Segments  Edges
unique id and unique name
Street Segments  Edges
unique id only
ids for intersections & street segments overlap  remember which is which in your code
Bloor & Yonge 1
215,000 street segments
24,500 streets 1
Bay & College 3
College & Spadina 4 2 3 4
DVP & unknown(20) 5 2
Bloor & Bay

3. Graph Type? Undirected or directed? One way streets  directed
A two way street makes 2 edges

4. Might also have “in_edge” list if you want/need it
Graph Representation?
Adjacency List or Adjacency Matrix? 1 2 3 4
Adjacency Matrix
Adjacency List
Node 0: out_edge {3}
Node 1: out_edge {0, 3, 2}
Node 2: out_edge {3, 4} …
To Node
Might also have “in_edge” list if you want/need it
From Node

5. Memory Complexity N intersections (N ~ 166,000 for Toronto)
Adjacency matrix:
N rows x N columns
Memory required: O(N2)
26 GB (for 1 byte / entry)!
Adjacency list:
N lists
Average: 4 ints / list
O(N)
2.6 MB! 1 2 3 4
Adjacency Matrix
To Node
Adjacency List
Node 0: out_edge {3}
Node 1: out_edge {0, 3, 2}
Node 2: out_edge {3, 4} …
From Node

6. libstreetsdatabase: More Than Connectivity
Intersections (Nodes) id
name
lattitude, longitude
StreetSegments (Edges)
Street id  What street are you part of?
This has a name
Speed limit
One way (from node  to node)
Curvepoints  shape of street segment

7. StreetSegment: Curve Points
Not all StreetSegments (city blocks) are straight
If not straight, have CurvePoints  list of (lat,lon) points followed between intersections

8. libstreetdatabase: Streets & POI
list of StreetSegments
unique id
unique name (e.g. “Yonge”)
Points of Interest id
location
non-unique name (e.g. “Tim Horton’s)
Natural Features
ponds, parks, etc.
Not used in milestone1

9. Graph Reference
Chapter 22 of Introduction to Algorithms by Cormen et al

10. Milestone 1 List of functions to implement in m1.h
Comments say what each should do
Good practice: documentation is in your code!
Header file: comments say how to use
Not how it is built
Detailed unit tests in ece297exercise
These give the detailed specification
“Test-driven development”
Most test functionality
Some also test speed  too slow  fail
One runs valgrind to check memory OK

11. Milestone 1 Unit Tests main.cpp (made by unit tests)
// Load anything you want here load_map (“toronto.bin”); int id = find_intersection_id_from_name (“Yonge & Bloor”); if (id != 22333) { <your code failed the test, record it> } // lots more tests // clean up here; all memory should be de-allocated close_map ();

12. load_map What should I do in load_map ()? 3 basic approaches
// Load anything you want here load_map (string map_name);
What should I do in load_map ()?
3 basic approaches
load_map does nothing
Implement all your higher-level api calls by calling lower level api (libstreetdatabaseapi) directly
Stateless
Often easier to code & debug
But may be slow for some calls
load_map builds everything you could ever want
Never have to call lower-level api again
You have full control  make beautiful, fast data structures

13. load_map Blended approach load_map creates some new data structures
// Load anything you want here load_map (string map_name);
Blended approach
load_map creates some new data structures
Use them for api calls that need them for speed
Call lower level api when it is fast enough
All 3 approaches are reasonable
Your choice which to use
If you fail speed tests, change your approach
load_map not automatically speed tested
Spec: keep speed interactive
Your TA will notice in the demo if it is very slow (> 1 s or so)
Otherwise OK

14. Clean Up
main.cpp
(made by unit tests)
// Load anything you want here load_map (“toronto.bin”); int id = find_intersection_id_from_name (“Yonge & Bloor”); if (id != 22333) { <your code failed the test, record it> } // lots more tests // clean up here; all memory should be de-allocated close_map ();
ece297exercise runs valgrind on a load_map(), use, close_map() test
Must free all memory or will lose marks

15. Automatic Memory Checking
Memory checking: valgrind slowdown ~10x
Testing: want fast & thorough
Small test case: almost as thorough as big
St. Helena

16. load_map  How Do I Get Its Data?
main.cpp
(made by unit tests)
// Load anything you want here load_map (“toronto.bin”); int id = find_intersection_id_from_name (“Yonge & Bloor”); if (id != 22333) { <your code failed the test, record it> } // lots more tests // clean up here; all memory should be de-allocated close_map (); ?
Easy way  global variable

17. But Aren’t Global Variables Bad?
Yes, if you overuse them
E.g. could pass argument but use global variable to avoid typing!
But almost all programs have some
Or something very similar
Limit their number
Group related data into classes (e.g. StreetGraph?)
 organizes data and avoids lots of namespace pollution
StreetGraph
find_intersection_id_from_name (“B & Y“);
load_map()
close_map()

18. Global Variable Pitfalls
StreetGraph *streetGraph; // Pointer to your data!
int find_intersection_id_from_name (string intersection_name) {
streetGraph->answerMe (intersection_name);
// What if streetGraph isn’t loaded yet?
// Crash!
delete streetGraph;
// Thought I should clean up, but my teammates will be // surprised when they try to use streetGraph next! }
Anyone can use / call functions of / delete our global object
Would be nice if we could check it was set up first

19. Object-Oriented Alternative
Design pattern: singleton
Have one loaded copy of a certain object
Many parts of the program need it
StreetGraph
find_intersection_id_from_name (“B & Y“);
load_map()
close_map()
When function asks for access
Return a pointer to the singleton object
But can check that it is loaded first

20. StreetGraph as a Singleton
class StreetGraph {
private:
static StreetGraph *theObjectPtr; // One copy per class
public:
StreetGraph (string mapName) {
if (theObjectPtr != NULL) {
cerr << “StreetGraph already loaded!” << endl;
. . . // take some action;
else {
... // Load up stuff
theObjectPtr = this; }
static StreetGraph *getObjectPtr ( ) {
if (theObjectPtr == NULL) {
cerr << “StreetGraph not loaded yet!” << endl;
. . . // could end the program, or could load stuff up
return (theObjectPtr);
Can call without an object
Replaces our global variable: like a controlled access global variable

21. Calling without an object  use full name
Singleton
StreetGraph.h
class StreetGraph {
...
public:
~StreetGraph () {
... // Clean everything up
theObjectPtr = NULL; // Says we’re not loaded }
somefile.cpp
#include “StreetGraph.h”
void myFunc ( ) {
StreetGraph *streetGraph = StreetGraph::getObjectPtr ();
streetGraph->someQuery ( ... );
... }
Calling without an object  use full name

22. Further Reading
Common problems, and how to map them to software designs
E.g. singleton pattern
Inspired by patterns in architecture

23. Team Formation
Dr. Tallman

24. ECE297 Tutorials, Jan 21 & Jan 23
Your team will meet your Communication Instructor (CI) and schedule a weekly 30-minute meeting beginning the following week.
Wed, Jan 21, 1-3pm, students go to GB404
Fri, Jan 23, 9-11am, students go to GB412
Fri, Jan 23, 3-5pm, students go to GB412
If you do not have a full team formed by these dates, come to your scheduled tutorial, and Dr. Tallman will assist you.