Added method to find constraints value for MILP

[verreld7]

Impelement new method to show the values of constraints of MILP according to the current variable's values. Based on #7300.

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have updated the documentation and checked the documentation preview.

[tscrim]

In addition, please add a test for a single integer input.

What happens when an index is outside of the valid input range?

[tscrim]

Suggested change

	sum = 0
	cons = self.constraints(i)[1]
	for index, coeff in zip(cons[0], cons[1]):
	sum += var_val[index] * coeff
	return sum
	s = 0
	cons = self.constraints(i)[1]
	for index, coeff in zip(cons[0], cons[1]):
	s += var_val[index] * coeff
	return s

Please avoid using builtin names like sum.

[tscrim]

Suggested change

	sum = 0
	cons = self.constraints(i)[1]
	for index, coeff in zip(cons[0], cons[1]):
	sum += var_val[index] * coeff
	return sum
	s = 0
	cons = self.constraints(i)[1]
	for index, coeff in zip(cons[0], cons[1]):
	s += var_val[index] * coeff
	return s

Please avoid using builtin names like sum.

[tscrim]

Suggested change

	indices = [n for n in range(0, self.number_of_constraints())]
	indices = [n for n in range(self.number_of_constraints())]

The 0 is unneeded in Python.

[tscrim]

Suggested change

	EXAMPLES:
	sage: p = MixedIntegerLinearProgram(maximization=True, solver='GLPK')
	EXAMPLES::
	sage: p = MixedIntegerLinearProgram(maximization=True, solver='GLPK')

and indent the rest accordingly.

[tscrim]

Suggested change

	[24.0, 6.0, -1.5, 1.5]
	"""
	[24.0, 6.0, -1.5, 1.5]
	"""

[tscrim]

Suggested change

	if isinstance(indices, (int, Integer)):
	result.append(calculate_value(self, indices))
	return result
	elif isinstance(indices, list):
	for i in indices:
	result.append(calculate_value(self, i))
	return result
	else:
	raise ValueError("constraints_values() requires a list of integers, though it will accommodate None or an integer.")
	elif indices in ZZ:
	indices = [ZZ(indices)]
	return [calculate_value(self, i) for i in indices]

[tscrim]

Suggested change

	from sage.rings.integer import Integer
	from sage.rings.integer_ring import ZZ

[tscrim]

I think you were too greedy with a find-replace sum -> result. Please revert almost all of those.

[tscrim]

Suggested change

	TESTS::
	TESTS:

[tscrim]

Suggested change

	ValueError: invalid row index 2
	"""
	from sage.rings.integer_ring import ZZ
	ValueError: invalid row index 2
	"""
	from sage.rings.integer_ring import ZZ

[tscrim]

Suggested change

	- ``indices`` -- select which constraint(s) values to return
	- If ``indices = None``, the method returns the list of all the
	constraints values.
	- If ``indices`` is an integer `i`, the method returns value of constraint
	`i`.
	- If ``indices`` is a list of integers, the method returns the list
	of the corresponding value of constraints.
	- ``indices`` -- select which constraint(s) values to return:
	* ``None`` - return the list of all the constraints values
	* an integer `i` - return the value of constraint `i`
	* a list of integers - return the list of the
	corresponding value of constraints

[github-actions]

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