Error thrown on simple equation

[victorBaro]

Thanks for this library, is working really well in many cases.

I am facing an issue though with a specific case:

        let solver: Solver = Solver()
        
        let row0 = Variable("row_0")
        let row1 = Variable("row_1")
        let row2 = Variable("row_2")
        let row3 = Variable("row_3")

        do {
            try solver.add(constraint: row0 == row1)
            try solver.add(constraint: row2 == row3)
            try solver.add(constraint: row0 + row1 + row2 + row3 == 240)
            try solver.add(constraint: row0 + row1 == 120)
            try solver.add(constraint: row2 + row3 == 120)
        } catch {
            throw error
        }

This simple equation is raising an error: caught error: "unable to satisfy constraint: 1.0 * row_2 + 1.0 * row_3 + -120.0 == 0

If I set any of the last 3 constraints as .strong (instead of required), the solver is able to resolve (all variable values are 60).

[nangege]

I am not sure how your code is actually written, but i add the following code to the unit test, it did pass the test."

func testSetRestricted2(){

let solver: SimplexSolver = SimplexSolver()

let row0 = Variable.restricted()
let row1 = Variable.restricted()
let row2 = Variable.restricted()
let row3 = Variable.restricted()

XCTAssertNoThrow(try solver.add(constraint: row0 == row1))
XCTAssertNoThrow(try solver.add(constraint: row2 == row3))
XCTAssertNoThrow(try solver.add(constraint: row0 + row1 + row2 + row3 == 240))
XCTAssertNoThrow(try solver.add(constraint: row0 + row1 == 120))
XCTAssertNoThrow(try solver.add(constraint: row2 + row3 == 120))

XCTAssertNoThrow(try solver.solve())

XCTAssertEqual(solver.valueFor(row0) , 60)
XCTAssertEqual(solver.valueFor(row1) , 60)
XCTAssertEqual(solver.valueFor(row2) , 60)
XCTAssertEqual(solver.valueFor(row3) , 60)

}