summing over multiple indices

[eric]

Hi, sorry for the simple question, but I'm new to pulp and not that
good at python yet. (I'll be happy to rtfm if someone tells me where
to look.)

I have a 3 dimensional variable:

self.x = LpVariable.dicts("x",(docs, days, shifts),
0,1,LpInteger)

and related costs (using a numpy array)

self.xc = zeros((ndocs,ndays,nshifts))

and I want to add the objective function where I multiply each x by
it's corresponding c.
How do I do that?

More generally, how do I use lpsum over multiple indices?

thanks,
Eric

[Stuart Mitchell]

ok there is a little thing to remember that pulp.LpVariable.dicts
generates dictionaries of dictionaries so the following is possible

>>> import pulp
>>> docs = ['a','b','c']
>>> days = ['mon','tue', 'wed']
>>> shifts = [0,1,2,3]
>>> x = pulp.LpVariable.dicts('x',(docs,days,shifts),0,1,pulp.LpInteger)
>>> x['a']['mon'][3]
x_a_mon_3

but the numpy array can only index by integers so the following is required.

>>> import pulp
>>> docs = [0,1,2]
>>> days = [0,1,2,3,4]
>>> shifts = [0,1,2,3]
>>> x = pulp.LpVariable.matrix('x',(docs,days,shifts),0,1,pulp.LpInteger)
>>> x[1][1][2]
x_1_1_2
>>> c = numpy.zeros((len(docs),len(days),len(shifts)))
>>> c[1][1][2]
0.0
>>> c[(1,1,2)]
0.0
>>> pulp.lpSum([c[doc][day][shift] * x[doc][day][shift]
... for doc in docs
... for day in days
... for shift in shifts])
0

Note the solution expression is zero as the c matrix is all zero

Stu

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Dr Stuart Mitchell
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Light Metals Research Centre (LMRC)
University of Auckland
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[eric]

Thanks! That works great.

Eric