# Questions tagged [pyomo]

For questions related to the Python optimization modeling package Pyomo.

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### Obtaining linear relaxation objective value from MILP model coded in Pyomo

I would like to seek some advice on modeling the following: I am currently using Pyomo to generate my MILP model in Pyomo. It seems that it is not possible to cast the integer and binary variables to ...
81 views

### How to display results of Pyomo variables in a pandas dataframe

I would like to display all the results of Pyomo variables in a pandas dataframe. I had a look at this question Pyomo: Looping Over A Variable Method and tried to adjust it to my case without success. ...
47 views

### Mutable parameter in Pyomo causes a problem

I am defining a Pyomo model that should have some mutable Big-M parameters whose values should be dynamically assigned (once). However, I am having a problem with a difference equation as described in ...
149 views

### How to find out which constraint causes problems in Pyomo

I have a Pyomo model with many constraints and variables. When solving it with Gurobi, I get the message "Model is infeasible or unbounded". Now I would like to find out which constraints ...
74 views

### Use if-statements when defining a constraint in Pyomo

I would like to define the value of a variable model.variable_costsPerTimeSlot [t] in pyomo and I would like to use if-statements. Depending on the value of the if-...
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### Correct way to define constraints in Pyomo

Can I know if the constraint below can be defined as follows in Pyomo for convex optimization. W and G are arrays of dimension M x N. ...
37 views

### Can I define constraints in Pyomo as a list?

I would like to define the following constraint in Pyomo $$W^\top{\bf 1}\le\hat w=\begin{bmatrix}\hat{w}_1&\hat{w}_2&\ldots&\hat{w}_N\end{bmatrix}^\top$$ where $W$ is a $2\times4$ matrix. ...
21 views

### Model definition in pyomo to solve online optimization problem

I am trying to model the attached online optmization problem in pyomo. Eventually, I am going to use the octeract solver to find the matrix soluions of W and G. I would like to ask advice about ...
50 views

### How to assign a single value to Pyomo parameter without a dictionary

I would like to assign a single value to a paramter that depends on a created set in Pyomo. I have the following code: ...
115 views

### Pyomo can't find Gurobi solver

I have a pyomo model that I can solve using the GLPK solver by just using the code: ...
76 views

### PYOMO - Optimization for the daily production of a products demand minimizing the production cost

I am trying to build an optimization model using PYOMO for the daily production of a product demand, minimizing the production cost. I have demand, production capacity (by machine by day), production ...
104 views

### Referencing of sets in Pyomo objectives

I have a question about referecing set in Pyomo objectives. Basically I have 2 options and I do not understand why one of it works whereas the other yields an error. Here you see them: ...
72 views

### How to display results from a solver during solving in Pyomo

I would like to see the current results (e.g. MIP gaps) of a solver in pyomo (as in GAMS) while solving the problem. I read that I should use the option "stream-solver" (see for instance ...
52 views

### How to implement a difference equation in Pyomo

I would like to define a difference equation in pyomo for a temperature variable. The equation (simplified) looks like: $Temperature(t) = Temperature (t-1) + x(t)$ , for t>0 $Temperature (0) = 20$ ...
59 views

### How to dynamically set variable names in Pyomo?

I am looking to set variables in my Pyomo model by using a loop, so that they can be created automatically. However, each variable also contains bounds. I was hoping that it can loop through a ...
192 views

### Pyomo can't find solver

I am new to Pyomo and I have the following optimization problem (original transport problem by Dantzig): ...
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### How to define constraints in Pyomo using sets and variables

I am trying to model the transportation problem of Dantzig in Pyomo (see the GAMS code here https://www.gams.com/latest/gamslib_ml/libhtml/gamslib_trnsport.html or the description here https://www....
98 views

### Why functions with arguments can be called without arguments in Pyomo

I have a question regarding pyomo. I have seen quite often, that for the definition of parameters, objectives and constraints, explicit functions are defined. These functions expect some arguments and ...
154 views

### Error when defining variables in Pyomo

I just started to learn about Pyomo. In several tutorials it is stated that the command for creating a variable is just model.Variable = VAR(...). However, I get ...
49 views

### Find multiple solutions in Pyomo with Gurobi

I am fairly new to Pyomo and Gurobi. I'd like to find 20 sets of different solutions that meet the following constraints. ...
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### Ipopt (probably) fails to solve a nonlinear problem, what is next?

I am trying to solve a nonlinear problem with only a set of continuous variables (where the nonlinearity stems from negative inconsistent - across differently indexed variables - large powers), e.g., ...
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### How to generate multiple solutions to linear program in Python?

I recently posted a question here where I had written some Pyomo code to solve a simple linear program, however I feel the Operations Research platform is perhaps a better fit for this question. My ...
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### How to collect solutions within CPLEX and retrieve them from PYOMO?

I would like to seek some advice on modeling the following: I am currently to invoke solvers, CPLEX, in particular. As I am solving my problem sequentially, i.e., the top-level subproblem results are ...
166 views

### Pyomo + Ipopt. Speed Issue

I am using Pyomo + Ipopt as solver to solve a NLP problem. The problem is not extremely complex in terms of dimensionality and ...
81 views

### Pyomo variable creation dilemma

I am working on a pyomo model, and need to create a few different sets of variables that are dependent on a solution from a master model. I need the variables to be indexed variables however the ...
519 views

### Can I use 'SCIP' solver for PYOMO?

I have an MINLP problem to solve where I was initially using 'ipopt' solver but the solution was not sticking to 'binary/boolean/integer' domain type for a variable. I am not sure which free solver ...
316 views

### Failing to meet a constraint in a NLP problem

I have a NLP problem at hand, which I am trying to solve via Pyomo + ipopt. I try to run several different instances of the optimizer with different conditions, out ...
264 views

### Can GLPK be used to solve an optimal team selection problem?

My Problem I am quite new to optimisation, so any advice is appreciated. I am currently trying to solve a problem as follows: Given a pool of people, we want to create n teams such to find the optimal ...
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### Provide basic solution to CLP

I'm using Pyomo to formulate an LP with approx 500,000 constraints and 200,000 decision variables. The LP is solved using CLP. Some instances fail to return even a feasible solution after many ...
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### Does pyomo support column generation?

I want to use column generation technique to solve cutting stock problem. Is there any other python modeling library that supports column generation?
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### CPLEX keeps restarting in Pyomo

I tried running my model by adding the following settings to CPLEX. ...
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### knapsack problem with non-linear constraint

I have a basic knapsack problem where I need to fit the most weight possible in a bin: ...
209 views

### Possibility of indexing decision variables with 2 indices using a set of tuples in Pyomo

I am currently attempting to solve a network problem that is not fully connected.Thus, I have attempted to do some preprocessing of data so as to form a set of tuples, e.g. $\{(a,b), (c,e),\ldots\}$, ...
158 views

### View of Constraints and Decision Variables in Pyomo

I have just attempted to construct my first Pyomo model. However, I was unable to locate any documentation that shows how to view constraints, decision variables. As my model is big, I need to see ...
98 views

### Pyomo: Help setting up my model

I have been working with a model for the past couple of weeks, but I am not sure what am I doing wrong as every time Pyomo returns that is infeasible or ...
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### Pyomo: Struggling to get a constraint to work

I am trying to model an Electric Vehicle scheduling to minimise the electricity bill. Of course, the EV will only be able to charge every time that is plugged into a charging station (i.e. it cannot ...
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I have just installed Anaconda and am intending to use Spyder as it is able to display variable, parameter values for debugging. After which, I am planning to use Pyomo to code my MIP model and invoke ...
470 views

### how to implement a constraint with max/min function in pyomo

I am implementing a NLP problem in pyomo, and I am getting some issues for this constraint: \forall i \in \lbrace 1, N \rbrace , \forall j \in \left\{1, M \right\}: Y_{i,j} \cdot ...
216 views

### Pyomo add constraint error: Rule failed when generation expression for constraint

I am trying to solve a model with Pyomo and struggling with indexing. Below is a simple problem instance, where you can also see the error. The message is straightforward and self-explanatory but ...
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### Model Simulation in PYOMO

I have an optimization model that I have developed within the PYOMO framework and I am unable to solve the model in a reasonable amount of time using the BARON solver. I have been instructed not to ...
119 views

### How to define hybrid variables without using additional binary variables?

I am working on a large NLP model with equilibrium equations in which the variables are defined in the following form: x_i \in [L_B, U_B] \cup\{0\} \quad \text{where} \quad L_B \ \& \ U_B \in\...
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### Rolling Horizon in Pyomo

I am trying to figure out how one could write a rolling horizon algorithm in PYOMO to speed up the solution of a model that I am building. My understanding of the Rolling Horizon Algorithm is that you ...
101 views

### BARON Error: variables/rows fixed as scaled bounds too close

I am trying to build my model up and keep running into this output from BARON: Clp0019I {x} variables/rows fixed as scaled bounds too close. I checked the BARON ...
661 views

### Modeling and solvers

I have just started to dive into OR world on my work. Currently we are using GAMS with Gurobi but some of us have strong programming background and would like to have more programmatic approach to OR. ...
133 views

### Pyomo CBC 1.#j error

I am using to solve my model Pyomo/CBC combination. But rarely, CBC Gap shows 1.#j and pyomo generate an error. Hence, it doesn't get solution. How can I solve this problem? Screen output: ...
1k views

### Reading an LP/MPS file using Pyomo software

I would like to know is it possible to read an LP/MPS file into the Pyomo software and solve the problem? If so, how can I do that?