I designing a polynomial class for one of my com sci courses , I have a problem of getting the integration method right can some one help me with that
/** The polynomial class includes the methods: evaluate , add, multiply,
* Differentiate , integrate and square root.
*/
public class polynomial {
private int degree;
private double[] coefficients;
// a constructor that creates a polynomial of degree degMax with all the coefficients are zeroes
public polynomial(int degMax) {
degree= degMax;
coefficients = new double[degree + 1];
}
// a setter method that let the users set the coefficients for the polynomial they constructed
public void setCoefficient(int d , double v ){
if (d > degree)
{
System.out.println("Erorr Message: the degree you specified is larger than the polynomial's degree that you have created ");
}
else {
coefficients[d]=v;
}
}
// a getter method to return the coefficient for the specified degree
public double getCoefficient(int i){
return coefficients[i];
}
// private method that counts the degree of the polynomial by searching for the last element in the coefficient array that
// does not contain zero
private int getDegree() {
int deg = 0;
for (int i = 0; i < coefficients.length; i++)
if (coefficients[i] != 0) deg = i;
return deg;
}
// a method that print out the polynomial as a string
public String print(){
if (degree == 0) return "" + coefficients[0];
if (degree == 1) return coefficients[1] + "x + " + coefficients[0];
String s = coefficients[degree] + "x^" + degree;
for (int i = degree-1; i >= 0; i--) {
if (coefficients[i] == 0) continue;
else if (coefficients[i] > 0) s = s + " + " + ( coefficients[i]);
else if (coefficients[i] < 0) s = s + " - " + (-coefficients[i]);
if (i == 1) s = s + "x";
else if (i > 1) s = s + "x^" + i;
}
return s;
}
// a method that evaluate the polynomial at specified value x
public double evaluate(double x) {
double result = 0;
for (int i = degree; i >= 0; i--)
result = coefficients[i] + (x * result);
return result;
}
// a method that perform symbolic addition of two polynomial
public polynomial addition(polynomial p2) {
polynomial p1 = this;
polynomial p3 = new polynomial(Math.max(p1.degree, p2.degree));
for (int i = 0; i <= p1.degree; i++) p3.coefficients[i] += p1.coefficients[i];
for (int i = 0; i <= p2.degree; i++) p3.coefficients[i] += p2.coefficients[i];
p3.degree = p3.getDegree();
return p3;
}
// a method that performs a symbolic multiplication
public polynomial multiply(polynomial p2) {
polynomial p1 = this;
polynomial p3 = new polynomial(p1.degree + p2.degree);
for (int i = 0; i <= p1.degree; i++)
for (int j = 0; j <= p2.degree; j++)
p3.coefficients[i+j] += (p1.coefficients[i] * p2.coefficients[j]);
p3.degree = p3.getDegree();
return p3;
}
// a method that apply differentiation to polynomial
public polynomial differentiate() {
if (degree == 0) return new polynomial(0);
polynomial derivative = new polynomial(degree - 1);
derivative.degree = degree - 1;
for (int i = 0; i < degree; i++){
derivative.coefficients[i] = (i + 1) * coefficients[i + 1];
}
return derivative;
}
// a method that find a polynomial integral over the interval a to b
public double integration(double a , double b) {
polynomial integral= new polynomial (degree+1);
integral.degree= degree+1;
for (int i=0 ; i<= degree+1 ; i++){
if (i==0) {
integral.coefficients[i]= 0;
}
else {
integral.coefficients[i]= (coefficients[i-1]/i);
}
}
return (evaluate(b)- evaluate(a));
}
public static void main(String[] args) {
polynomial p1 = new polynomial(3);
p1.setCoefficient(0, 3.0);
p1.setCoefficient(3, 5.0);
String r = p1.print(); //3.0 + 5.0 x^3
polynomial p2 = new polynomial(2);
p2.setCoefficient(1, 4.0);
p2.setCoefficient(2, 2.0);
polynomial n = p1.addition(p2);
String po = n.print();
polynomial t = p1.multiply(p2);
String tr = t.print();
polynomial di = p2.differentiate();
String dir = di.print();
double ev = p2.evaluate(5.0);
double inte = p1.integration(3.0, 7.0);
System.out.println("p1(x) = " + r );
System.out.println("p1(x) + p2(x) = " + po);
System.out.println("p1(x) * p2(x) = " + tr);
System.out.println("p2'(x) = " + dir);
System.out.println("p1(x) integration over [3.0, 7.0] = " + inte);
System.out.println("p2(5.0) = " + ev);
}
}
If I were you, I would split the methods :
public Polynomial integrate()
{
Polynomial integral = new Polynomial(this.degree + 1);
for (int i = 1; i <= this.degree+1; i++)
{
integral.coefficients[i] = (this.coefficients[i - 1] / i);
}
return integral;
}
// a method that find a Polynomial integral over the interval a to b
public double integration(double a, double b)
{
Polynomial integral = integrate();
return (integral.evaluate(b) - integral.evaluate(a));
}
Ok now why it didn't work as you expected :
public double integration(double a , double b) {
polynomial integral= new polynomial (degree+1);
integral.degree= degree+1;
for (int i=0 ; i<= degree+1 ; i++){
if (i==0) {
integral.coefficients[i]= 0;
}
else {
integral.coefficients[i]= (coefficients[i-1]/i);
}
}
return (evaluate(b)- evaluate(a));
}
you messed up your "integral" object with the current instance "this", clean your code first :
public double integration(double a , double b) {
polynomial integral= new polynomial (this.degree+1);
integral.degree= this.degree+1;
for (int i=0 ; i<= this.degree+1 ; i++){
if (i==0) {
integral.coefficients[i]= 0;
}
else {
integral.coefficients[i]= (this.coefficients[i-1]/i);
}
}
return (this.evaluate(b)- this.evaluate(a));
}
Here you can see that you evaluate on your instance object instead of "integral" object. That's why it messed up the result.