Adding polynomials

Question

I need some help. I am doing test-driven development. These are the tests:

@Test public void add01() throws TError { assertEquals(new Term(10,5),  new Term(4,5).add(new Term(6,5))); }
@Test public void add02() throws TError { assertEquals(new Term(6,5),   new Term(0,5).add(new Term(6,5))); }
@Test public void add03() throws TError { assertEquals(new Term(2,5),   new Term(-4,5).add(new Term(6,5))); }
@Test public void add04() throws TError { assertEquals(new Term(10,0),  new Term(4,0).add(new Term(6,0))); }
@Test public void add05() throws TError { assertEquals(new Term(4,5),   new Term(4,5).add(new Term(0,5))); }
@Test public void add06() throws TError { assertEquals(new Term(-2,5),  new Term(4,5).add(new Term(-6,5))); }

@Test (expected = IncompatibleTerms.class)
public void add07() throws TError { t = new Term(4,5).add(new Term(6,0)); }

@Test (expected = CoefficientOverflow.class)
public void add08() throws TError { t = new Term(min,4).add(new Term(-1,4)); }

@Test public void add09() throws TError { assertEquals(new Term(min,4), new Term(min+1,4).add(new Term(-1,4))); }
@Test public void add10() throws TError { assertEquals(new Term(-11,4), new Term(-10,4).add(new Term(-1,4))); }
@Test public void add11() throws TError { assertEquals(new Term(-2,4),  new Term(-1,4).add(new Term(-1,4))); }
@Test public void add12() throws TError { assertEquals(new Term(-1,4),  new Term(0,4).add(new Term(-1,4))); }
@Test public void add13() throws TError { assertEquals(Term.Zero,       new Term(1,4).add(new Term(-1,4))); }
@Test public void add14() throws TError { assertEquals(new Term(9,4),   new Term(10,4).add(new Term(-1,4))); }
@Test public void add15() throws TError { assertEquals(new Term(max,4), new Term(max-1,4).add(new Term(1,4))); }

@Test (expected = CoefficientOverflow.class)
public void add16() throws TError { t = new Term(max,4).add(new Term(1,4)); }

//Using domain-specific knowledge:  addition should be commutative

@Test public void add17() throws TError { assertEquals(new Term(-1,2).add(new Term(1,2)),       new Term(1,2).add(new Term(-1,2))); }
@Test public void add18() throws TError { assertEquals(new Term(min+1,2).add(new Term(-1,2)),   new Term(-1,2).add(new Term(min+1,2))); }
@Test public void add19() throws TError { assertEquals(new Term(min,2).add(Term.Zero),      Term.Zero.add(new Term(min,2))); }
@Test public void add20() throws TError { assertEquals(new Term(min,0).add(Term.Unit),      Term.Unit.add(new Term(min,0))); }
@Test public void add21() throws TError { assertEquals(new Term(max,0).add(Term.Zero),      Term.Zero.add(new Term(max,0))); }
@Test public void add22() throws TError { assertEquals(new Term(max-1,2).add(new Term(1,2)),    new Term(1,2).add(new Term(max-1,2))); }
@Test public void add23() throws TError { assertEquals(new Term(max,2).add(new Term(min,2)),    new Term(min,2).add(new Term(max,2))); }

This is my add method so far with the help of "Andrej Gajduk".

public Term add(Term that) throws CoefficientOverflow, IncompatibleTerms {
    if (this.expo != that.expo) throw new IncompatibleTerms();
    return new Term (this.coef + that.coef,expo);
}

These are the tests that fail = 2, 5, 8, 12, 16, 19, 21. But I have doubts about tests 17-23; I know some of them pass but I don't think they should because that is like x + y = y + x, but I am not sure how to implement it.

I need some help/guidance on why this tests are failing.

For tests 8 and 16 I have tried the code below. It does the job but then it creates more errors on the other tests. So then all together the fails become 2, 5, 8, 12, 16, 19, 21 + 20, 23 (two extra fails)

if (this.coef == Integer.MIN_VALUE || that.coef == Integer.MIN_VALUE) throw new CoefficientOverflow();
if (this.coef == Integer.MAX_VALUE || that.coef == Integer.MAX_VALUE) throw new CoefficientOverflow();

Can you post your `Term.equals()` method? – John Kugelman Nov 17 '12 at 20:40 — John Kugelman, Nov 17 '12 at 20:40
This is not test-driven development. – Don Roby Nov 17 '12 at 20:44 — Don Roby, Nov 17 '12 at 20:44
y isit not test driven development? – Lax Nov 17 '12 at 20:49 — Lax, Nov 17 '12 at 20:49

score 0 · Answer 1 · answered Nov 17 '12 at 20:56

This link shows a different way to detect overflow: http://mindprod.com/jgloss/gotchas.html#OVERFLOW

I think it is because when the coef is 0 in either this or that the whole statement is assumed to be zero so you need to check this and use the alternative to that which is zero

if(this.coef ==0)
{//return Term t = new Term(that.coef, that.expo);}

else
{//return Term t = new Term(this.coef, this.expo);}
}

I hope this helps

Yogendra Singh · Accepted Answer · 2012-11-17T22:39:50.753

0

Your equals method is incorrect. Please update it as below:

@Override
public boolean equals(Object that) {
    if (that == null) {
        return false;
    }else if (this.getClass() != that.getClass()) {
        return false;
    }else if (this == that) {
        return true;
    }else{
        Term term = (Term) that;
        if ((term.coef) == (this.coef) && (term.expo) == (this.expo)) {
            return true;
        }
    }
    return false;
}

To make you most of the test cases pass, update the add method as below:

public Term add(Term that) throws IncompatibleTerms, CoefficientOverflow{
    //handle addition with term zero
        if(this.equals(Term.Zero)){
        return that;
    }else if(Term.Zero.equals(that)){
        return this;
    }

    if (this.expo != that.expo) throw new IncompatibleTerms();
    if((this.coef>= 0 && that.coef >= 0 && this.coef + that.coef <0) ||
            (this.coef<= 0 && that.coef <= 0 && this.coef + that.coef >0)){
                         throw new CoefficientOverflow();
        }    
    return new Term (this.coef + that.coef,expo);
}

edited Nov 17 '12 at 22:39

answered Nov 17 '12 at 20:58

Yogendra Singh

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@Lax: I made some updates in the answer. Please check and let me know, if this doesn't help. – Yogendra Singh Nov 17 '12 at 21:30
thanks for ur help it does pass most of the tests except 7,8 & 16 am trying to figure out y 7 has failed because the condition for different exponent is correct – Lax Nov 17 '12 at 21:52
@Lax: For me, all the test cases are passing. Do you have some special constructor method? – Yogendra Singh Nov 17 '12 at 21:59
public Term(int c, int e) throws NegativeExponent { if (e < 0) throw new NegativeExponent(); coef = c; expo = (coef == 0) ? 1 : e; } – Lax Nov 17 '12 at 22:03
@Lax: I used the same and all test cases are passing. Just to check, are you using the updated `equals` method from the answer. There was an issue and I updated that sometime back. – Yogendra Singh Nov 17 '12 at 22:19
i see but much appreciated for the help you have provided thank you very much ill try to review my constructor and thanks for correcting my equals method as well – Lax Nov 17 '12 at 22:19
@Lax: Updated the equals method again. – Yogendra Singh Nov 17 '12 at 22:39

Adding polynomials

2 Answers2