Formulating an LP problem (Mathematics/Engineering)

  • Thread starter bobbo7410
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In summary, the conversation discusses the general idea behind LP constraints and whether variables can be on both sides of a constraint. It is mentioned that for matrix methods, all variables should be on one side and the constant on the other. The conversation also mentions the importance of understanding and properly following these constraints for problem-solving.
  • #1
bobbo7410
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Homework Statement



I don't exactly have a specific example, I'm looking for the general idea behind LP constraints.

Homework Equations



Within the constraints, do the variables have to be all to one side?

For instance, X1 + 2 > 3 is a standard constraint

would for example

X1 + 2 > X1 + 1

still be acceptable as a constraint?
 
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  • #2
bobbo7410 said:

Homework Statement



I don't exactly have a specific example, I'm looking for the general idea behind LP constraints.

Homework Equations



Within the constraints, do the variables have to be all to one side?

For instance, X1 + 2 > 3 is a standard constraint
This would normally be written as x1 > 1. Did you mean x1 + 2x2 > 3?
bobbo7410 said:
would for example

X1 + 2 > X1 + 1

still be acceptable as a constraint?
No. This is equivalent to 2 > 1, which is always true, so doesn't constrain things in any way. Did you mean x1 + 2 > x2 + 1?

That could be written as x1 - x2 > -1
 
  • #3
I'm sorry, it was late and my examples are horrible. They do not confine to standard constraints, they were simply just numbers to illustrate.

The basic question is, can you have variables on both sides of a constraint? Or must the variables be confined to one side?
 
  • #4
You can always move variables from one side of an equation/inequality to the other.
 
  • #5
Mark44 said:
You can always move variables from one side of an equation/inequality to the other.

Yes I understand that, my question is, must I?

I recently took a test, and after looking through the examples, they set the constraints equal to 0 and isolated all the variables to one side. I left the constraints with variables on both sides. Not sure if I would get points off for doing so...
 
  • #6
To use matrix methods (e.g., Simplex tableau), you need to have all the variables on one side, and the constant on the other. I'm pretty sure this is correct, although I haven't done one of these problems for a good long while.
 
  • #7
Mark44 said:
To use matrix methods (e.g., Simplex tableau), you need to have all the variables on one side, and the constant on the other. I'm pretty sure this is correct, although I haven't done one of these problems for a good long while.

Gotcha yeah, that makes sense. I suppose it wouldn't be completely incorrect, yet not properly done. Anyway I'll find out soon enough.

Thanks for your help!
 

1. What is the purpose of formulating an LP problem?

The main purpose of formulating an LP (Linear Programming) problem is to find the optimal solution to a real-world problem. This involves maximizing or minimizing a linear objective function while satisfying a set of linear constraints.

2. What are the steps involved in formulating an LP problem?

The steps for formulating an LP problem are as follows: 1. Define the decision variables2. Write the objective function3. Write the constraints4. Identify any additional conditions or restrictions5. Convert the problem into standard form (if necessary)

3. What is the difference between a decision variable and a constraint in an LP problem?

A decision variable is a quantity that the decision maker can control or change in order to achieve the desired outcome. On the other hand, a constraint is a limitation or restriction on the decision variables that must be satisfied in order to find a feasible solution to the problem.

4. How do you know if an LP problem has a feasible solution?

An LP problem has a feasible solution if there exists at least one combination of decision variable values that satisfies all of the constraints. This can be determined by graphing the constraints and finding the feasible region, or by using a computer program to solve the problem.

5. What are some real-world applications of LP problems?

LP problems have a wide range of applications in different fields, including engineering, economics, transportation, and resource allocation. Some examples of real-world applications include production planning, portfolio optimization, diet planning, and scheduling.

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