Pyomo summation of a product of a matrix by a vector

问题

I edit my code including all the parameters and variables involved:

(D is a numpy matrix imported from Python)

import pyomo
from pyomo.environ import *
from array import *


import numpy as np
import scipy as sp
from diff_matrix import D  ##N=10????
print(D)


m =ConcreteModel()
...
m.n = Param(initialize = 10, within = Integers)               
m.Ns = Set(initialize = range(0,value(m.n)))   
m.x1 = Var(m.N, domain = Reals)
m.D = Param(m.N, m.N, initialize=D)

m.f_x1 = Var(m.N)
def f_x1_definition(model,i):
        return m.f_x1[i] == sum(m.x1[j]*m.D[i,j] for j in range(value(m.n)))
m.f_x1_const = Constraint(m.Ns, rule = f_x1_definition)

But I get the next error:

   ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

Any help?

回答1:

The simplest thing is to just use the Python sum() function instead of the Pyomo summation() function:

def f_x1_definition(model,i):
    return model.f_x1[i] == sum(model.x1[j]*model.D[i,j] for j in range(value(model.n)))

Also, note that I reversed the order of the Pyomo Var (m.x1) and the matrix (m.D). Based on your other questions (Importing a matrix from Python to Pyomo), I am assuming that the matrix is a NumPy matrix. When multiplying a NumPy value and a Pyomo component (Var or Param), always put the Pyomo object first. This is due to a conflict between the NumPy operator overloading and the Pyomo operator overloading in current versions of Pyomo (up through at least 5.1).

EDIT 1: Note on reversing the order of operands: in your original question, it was not clear that m.D was being defined as a Pyomo Param. There is no concern with the order of Pyomo objects in expressions. The operator overloading problem mentioned above is only when multiplying NumPy objects with Pyomo components. Further, at this time (up through Pyomo 5.1), Pyomo does not support matrix algebra - that is, operations like matrix-matrix or matrix-vector products. Since every expression is a scalar expression, the ordering of the terms in a commutative operation (+, *) does not change the meaning of the expression.

EDIT 2: Your error has nothing to do with the sum/summation you originally posted. The problem is with how you are initializing your Param. At this time (up through Pyomo 5.1), you cannot directly initialize a Param from a numpy.ndarray. You need to first convert the NumPy object into a Python dictionary with something like:

m.D = Param(m.N, m.N, initialize=dict(((i,j),D[i,j]) for i in m.N for j in m.N))

来源：https://stackoverflow.com/questions/41833664/pyomo-summation-of-a-product-of-a-matrix-by-a-vector

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matrix

pyomo