AN ENROLMENT PROJECTION PROBLEM

[Steven Taschuk]

Quoth Ajith Prasad:
> I would appreciate advice on how best to formulate the following
> problem in Python. [...]

If you really want to bring out the linear algebra guns, I'm sure
Numeric has everything you need.  But for a problem this simple,
I'd just write

    def enrollment(year, intake, survivalrate):
        return sum([intake[year-i]*rate
                    for i, rate in enumerate(survivalrate)])

That's for Python 2.3.  In 2.2 you could write

    def enrollment(year, intake, survivalrate):
        sum = 0
        for i in range(len(survivalrate)):
            sum = sum + intake[year-i]*survivalrate[i]
        return sum

In either case, using it might look something like this:

    # survivalrate[n] is proportion of students who survive n years.
    survivalrate = [1, 0.5, 0.25, 0.1]

    # intake[n] is the number of students intook in year n.
    actualintake = {
            1993: 980, 1994: 1019, 1995: 1038, 1996: 1046, 1997: 1043,
            1998: 970, 1999: 954, 2000: 980, 2001: 952, 2002: 1047,
        }
    plannedintake = {2003: 1000, 2004: 1000, 2005: 1100, 2006: 1200}

    intake = actualintake.copy()
    intake.update(plannedintake)

    print enrollment(2004, intake, survivalrate)

Note that the intake vectors are dicts, not lists; I do this so I
can avoid index-twiddling.  I find the code to be easier to read
and write this way.

-- 
Steven Taschuk                            staschuk at telusplanet.net
Every public frenzy produces legislation purporting to address it.
                                                  (Kinsley's Law)