How to generate a constraints via a loop

[ran tao]

hi, all

i want to create a set of constraints, as following:

Pg[0] <= Pmax[0]

Pg[1] <= Pmax[1]

Pg[3] <= Pmax[3]

Pg[4] <= Pmax[4]

Pg[5] <= Pmax[5]

and, my code is as following:

import pyomo.environ as pyo

model = pyo.ConcreteModel()
Ngen = 5
Pmax = [40, 170, 520, 200, 100]
model.Ngen = pyo.Set(dimen=Ngen)
model.Pg = pyo.Var(model.Ngen)

def Co1(model):
    return ((model.Pg[ii] for ii in model.Ngen) <= (Pmax[jj]  for jj in range(Ngen)))

model.Co1 = pyo.Constraint(rule=Co1)

but, the Python Console tells me:

" TypeError: '<=' not supported between instances of 'generator' and 'generator' "

HOW DO I RECORRECT this?

and the other quesiton, if the Pmax is not a list, but a numpy-ndarray. somethings will different?

thanks a lot!

[Lucas Ford]

Hi Ran, 

I believe what you are looking for is something like the following:

def Co1(model,ii):
    return model.Pg[ii] <= model.Pmax[ii]
model.Co1 = pyo.Constraint(model.Ngen, rule=Co1)

Where you will define model.Pmax as a parameter with dimension Ngen and initialize it to Pmax. This will allow pyomo to create the constraint for all indices in model.Ngen. 

Hope this helps. 

[Rob]

You're going to want to change your constraint to

def Co1(model, ii):

    return model.Pg[ii] <= Pmax[ii]

model.Co1 = pyo.Constraint(model.Ngen, rule=Co1)

Another way to do it, similar to your logic, would be:

model.Co1 = pyo.ConstraintList()

for ii in model.Ngen:

    model.Co1.add(model.Pg[ii] <= Pmax[ii])

On Friday, March 6, 2020 at 12:31:19 AM UTC-5, ran tao wrote:

[ran tao]

Hi Lucas

thanks for your answer!

something about obj and constraints may be correct in your way when i run the obj or constraints code singlely.

but when i try to solve this model, another question i encounter.

the Python Console tells me:

" ValueError: ERROR: No objectives defined for input model. Cannot write legal LP file. "

and my whole code is as following:

import pyomo.environ as pyo

import pyomo.opt as SolverFactory

model = pyo.AbstractModel()

Ngen = 5

pg = [10, 12, 13, 12, 15]

rg = [0., 0., 0., 0., 0.]

sumPd = 1000

Pmax = [40, 170, 520, 200, 100]

Pmin = [5, 20, 50, 20, 10]

model.Ngen = pyo.Set(dimen=Ngen)

model.Pg = pyo.Var(model.Ngen,domain=pyo.NonNegativeReals)

model.Rg = pyo.Var(model.Ngen,domain=pyo.NonNegativeReals)

model.Pmax = pyo.Param(model.Ngen,initialize=Pmax)

model.Pmin = pyo.Param(model.Ngen,initialize=Pmin)

model.pg = pyo.Param(model.Ngen,initialize=pg)

model.rg = pyo.Param(model.Ngen,initialize=rg)

def ObjRule(model, ii):  

  return (sum(model.Pg[ii] * model.pg[ii] + model.Rg[ii] * model.rg[ii]))

model.Obj = pyo.Objective(model.Ngen, rule=ObjRule)

 

def Co1(model, ii):  

  return (model.Pmin[ii] <= model.Pg[ii] <= model.Pmax[ii])

model.co1 = pyo.Constraint(model.Ngen, rule=Co1)

def Co2(model, ii):  

  return (model.Pg[ii] + model.Rg[ii] <= model.Pmax[ii])

model.co2 = pyo.Constraint(model.Ngen, rule=Co2)

def Co3(model, ii):  

 return (sum(model.Pg[ii]) == sumPd)

model.co3 = pyo.Constraint(model.Ngen, rule=Co3)

instance = model.create_instance()

opt = pyo.SolverFactory('glpk')

opt.solve(instance)

在 2020年3月6日星期五 UTC+8下午8:59:55，Lucas Ford写道：

[Cesar Silva]

I think the problem is your objective function definition. You should define the summation within the function that is returned, different from an indexed constraint. It should be:

def ObjRule(model):  

  return (sum(model.Pg[ii] * model.pg[ii] + model.Rg[ii] * model.rg[ii] for ii in model.Ngen))

model.Obj = pyo.Objective(rule=ObjRule)

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[ran tao]

Hi Cesar

thanks for your reply!

i try it in your way, and now the Python tells me :(it is NOT a error)

"

WARNING: Constant objective detected, replacing with a placeholder to prevent

    solver failure.

WARNING: Empty constraint block written in LP format - solver may error

"

so, i fix my all constraint as your method, but it may be wrong:

the error message is:

"

ValueError: Constraint 'co1' does not have a proper value. Found '<generator object Co1.<locals>.<genexpr> at 0x0000020B02BAAA98>'

Expecting a tuple or equation. Examples:

   sum(model.costs) == model.income

   (0, model.price[item], 50)

"

and the python function, i.e. def Co1(model, ii). the parameter ii makes me confused

i think i see this form in the Pyomo Document, but i cannot understand how it works, because no value pass to the parameter ii.

在 2020年3月6日星期五 UTC+8下午10:23:41，Cesar Silva写道：

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[Siirola, John D]

The problem is that your entire model is indexed by an empty Set.  You are declaring

 

model.Ngen = pyo.Set(dimen=5)

 

The “dimen” keyword tells Set to expect that each member of the Set will be a tuple with 5 elements.  However, you never actually provide any data to the Set.  I think what you want is a Set with 5 members, 0 through 4.  You can get that one of two ways:

 

                model.Ngen = pyo.Set(initialize=range(5))

or

                model.Ngen = pyo.RangeSet(0,4)

 

Also note that you are not initializing your Params incorrectly.  The Param initialize keyword expects a dictionary mapping index to value and not a list.  As written, each Param will get a value that is itself a list.

 

john

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[陶然(TAO Ran)]

finally，i success！

thank you vvvvvvery much！

'Siirola, John D' via Pyomo Forum <pyomo...@googlegroups.com> 于2020年3月6日周五 下午10:59写道：

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