Is this solution.json correct for input.json? (Bin Cutting Verification)

[ParthavK]

Hi everyone,

I’m working with the repository’s tools for the cutting stock / bin packing problem.
I have an example using the following files:

input_8.json

solution_8.json

Here is the visual layout generated:

In the second bin, I believe there could be a more optimal placement, or at least a different valid arrangement that fits better.
I’m not sure whether:

My understanding of the objective function is incorrect, or

I’m using the solver in the wrong way, or

The solver did not find the optimal solution for this instance.

Could someone please confirm whether this output is expected, or if I am missing a configuration/parameter related to optimization objectives?

Thank you!

[fontanf]

Hi,

You're using the variable-sized bin packing objective which only looks at the total cost of the bins used. See https://fontanf.github.io/packingsolver/objectives.html

With the bin packing with leftovers objective, I get the following solution:

[ParthavK]

Hi,

Sorry for the different inputs and output. Can you please check again.

[fontanf]

Could you show what the better solution you're thinking of looks like?

[ParthavK]

I think this solution is correct because it leaves a larger continuous leftover area in the bin, which will be useful for the next operations.

There is also another possible solution: moving all the smaller parts into one bin and the larger parts into another.

[fontanf]

The solver minimizes the area of this rectangle in the last bin

That is, it considers the leftover to be L-shaped. So the other solution might be slightly better

[ParthavK]

Okay.

But I want to maximize the value of left_bin_area/left_bin_perimeter. Can I achieve this through any objective function?

I want to use this for metal sheet cutting. In such jobs, both cutting cost and material cost are important.

If you check the system-generated output, you will notice that it often creates many unnecessary cuts.

Please tell me if you have any solution for this.

[fontanf]

But I want to maximize the value of left_bin_area/left_bin_perimeter

In this example, it seems easy. But in the general case, maximizing the perimeter or the area might give unsatisfactory results if the shape of the leftover is complex.

There's currently no other way to define the leftover value in the solver. But you can try to edit the code that computes it manually to see if you find something that fits your need

packingsolver/src/irregular/solution.cpp

Lines 107 to 108 in f1e2baa

	leftover_value_ = (bin_type.x_max - bin_type.x_min) * (bin_type.y_max - bin_type.y_min)
	- (x_max_ - bin_type.x_min) * (y_max_ - bin_type.y_min);