CODEWITHSUNDEEP
c++polynomial-math
Casper
Casper

Reputation: 1723

overload * operator to multiply 2 polynomials

I'm trying to write multiply 2 polynomials using overloading * operator

This is the overloading * func

Polynomial Polynomial::operator * (const Polynomial &right)
{
    Polynomial temp;
    temp.setPolynomial(right.maxExp + maxExp + 1);
    for (int i = 0; i < maxExp; i++)
    {
        for (int j = 0; j < right.maxExp; j++)
            temp.poly[1][i+j] += poly[0][i] * right.poly[0][j];
    }
    return temp;
}

The array result, where 1st row is the coefficients and the second row stores the exponents. 

The first (original) polynomial is: (degree = 4, F = x^2)
0 0 1 0 0
0 0 2 0 0
The second polynomial is: (degree = 4, F = x^2)
0 0 1 0 0
0 0 2 0 0
The result polynomial is: // the location of the result is right (x^4)
0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 1 0 0 0 0 0 0 0

Polynomial class

class Polynomial
{
private:
    int **poly;
    int maxExp;
    void createPolynomialArray(int);
public:
    Polynomial();
    Polynomial(int); // constructor
    Polynomial(const Polynomial &); // copy constructor
    ~Polynomial(); // destructor

    // setter
    void setCoefficient(int,int);
    void setPolynomial(int);

    // getters
    int getTerm() const; // get the maxExp (highest exponent)
    int getCoefficient(int,int) const; // get a specific exponential value

    // overloading operators
    void operator=(const Polynomial &); // assignment
    Polynomial operator+(const Polynomial &); // addition
    Polynomial operator-(const Polynomial &); // substraction
    Polynomial operator*(const Polynomial &);
}

Question: what's wrong with my code that it produces that values? Thanks!

Upvotes: 0

Views: 2828

Answers (1)

999k
999k

Reputation: 6565

With this you are updating the result exponent with multiple of coefficients;

 temp.poly[1][i+j] += poly[0][i] * right.poly[0][j];

I think the code should be 

for (int j = 0; j < right.maxExp; j++)
{
    temp.poly[0][i+j] += poly[0][i] * right.poly[0][j];
    if (temp.poly[0][i+j] != 0)
        temp.poly[1][i+j] = i+j;
}

Also i think in your code storing exponents is redundant information as position in array itself reflects the exponent

Upvotes: 1

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