Optimization program using Lagrange multipliers.

In summary, the problem is about finding numbers x, y, and z that maximize 8xyz, given the constraint x^2+ y^2+ z^2= r^2. The original problem did not mention x, y, and z, so a coordinate system was set up with the center of the sphere as origin and axes parallel to the sides of the rectangular solid. The coordinates of the vertex in the first octant were taken as x, y, and z, making it clear that they are positive. Negative values would be acceptable if the problem were just to find numbers x, y, and z satisfying x^2+ y^2+ z^2= r^2, but in this case, there would
  • #1
theBEAST
364
0

Homework Statement


Here is the problem, the solution and my question (in red):
YPtQ50N.png


I'm guessing it was rejected because for the volume function, the dimensions cannot be negative? What if it was not volume and instead was just an arbitrary function. In that case you would not reject anything right?

Thanks!
 
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  • #2
I do not think your constraint really corresponds to the problem. x, y, z are dimensions of the box, not coordinates of any of its points.
 
  • #3
theBEAST said:

Homework Statement


Here is the problem, the solution and my question (in red):
YPtQ50N.png


I'm guessing it was rejected because for the volume function, the dimensions cannot be negative? What if it was not volume and instead was just an arbitrary function. In that case you would not reject anything right?

Thanks!
Yes, if the problem were just to find numbers x, y, and z, satisfying [itex]x^2+ y^2+ z^2= r^2[/itex], that maximize 8xyz, then negative values would also be acceptable. There would, in fact, be 8 different solutions.

Personally, I think the solution given is a little "terse". Because the original problem made no mention of x, y, and z, I would have started: "Set up a coordinate system having the center of the sphere as origin and axes parallel to the sides of the rectangular solid. Take "x", "y", and "z" to be the coordinates of the vertex in the first octant."

That would make it clear that x, y, and z are positive.
 

Related to Optimization program using Lagrange multipliers.

1. What is an optimization program using Lagrange multipliers?

An optimization program using Lagrange multipliers is a mathematical technique used to solve constrained optimization problems. It involves finding the maximum or minimum value of a function subject to constraints, using a set of equations called the Lagrangian equations. This method is commonly used in economics, engineering, and other fields.

2. How does the Lagrange multiplier method work?

The Lagrange multiplier method involves finding the partial derivatives of the objective function and the constraints, and then setting them equal to each other. This creates a system of equations that can be solved to find the optimal values for the variables. The Lagrange multiplier, which is a scalar value, is used to account for the constraints and ensure that the solution is valid.

3. What are the advantages of using Lagrange multipliers for optimization?

One advantage of using Lagrange multipliers is that it can handle both equality and inequality constraints. This means that it is a versatile method that can be applied to a wide range of optimization problems. Additionally, it provides a way to incorporate constraints into the optimization process without having to modify the objective function.

4. Are there any limitations to using Lagrange multipliers for optimization?

One limitation of the Lagrange multiplier method is that it can only be used for differentiable functions. This means that it may not be applicable to all types of optimization problems. Additionally, it may not always give the global optimal solution, but rather a local optimum.

5. Can the Lagrange multiplier method be extended to handle multiple constraints?

Yes, the Lagrange multiplier method can be extended to handle multiple constraints. This involves creating a Lagrangian function that includes all of the constraints and using the partial derivatives of this function to find the optimal solution. This method is also known as the Lagrangian multiplier method or the method of undetermined multipliers.

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