I need help: Time is limited. Due tomorrow!

[GolfinRover]

This is probably the worst prof I have ever had so I have no idea what to do to make this program. Help would be greatly appreciated.


Specifications:

Function poly(given x, z, a, b, c; returns y)

Function roots(given degree, left, right, z, a, b, c, &secondRoot; returns estimateOfRoot)

Note: The roots function has a switch structure to process either a polynomial of degree 2 or 3 with case 2: to handle quadratic formula that returns two roots, one through the normal return statement via estimateOfRoot and a second root through the reference parameter &secondRoot; and with case 3: to handle the cubic polynomial with the incremental search technique.

Your main module should drive the roots function with PIE from the user for degree, coefficients, interval limits, and step size until the user decides to quit the program with a value of -1 for degree, that is, an input sentinel of -1 to terminate a loop in the main module that drives your Polynomial Roots Problem.

[gpraghuram]

We cant write the code for you.
Tell us what problem u are facing with this.

Raghu

[GolfinRover]

Here, I wrote psuedocode for it. Does this seem correct?

Main: read coefficients, interval endpoints a and b,
and step size
compute the number of subintervals, n
set k to 0
while k<= n-1
compute left subinterval endpoint
compute right subinterval endpoint
check_roots (left, right, coefficients)
increment k by 1
check_roots (b, b, coefficients)
check_roots (left, right, coefficients);
set f_left to poly(left, coefficients)
set f_right to poly(right, coefficients)
if f_left is near zero
print root at left endpoint
else
if f_left * f_right < 0
print root at midpoint of subinterval
return
poly(x,a0,a1,a2,a3);
return a0x^3 + a1x^2 + a2x + a3

New Function

#include <iostream>
#include <cmath>
Using namespace std;
int main()
{
int n;
double a0, a1, a2, a3, a, b, step, left, right;
cout<<”Enter coefficients a0, a1, a2, a3: \n”;
cin>>a0>>a1>>a2>>a3;
cout<<”Enter interval limits a, b (a<b): \n”;
cin>>a >>b;
cout<<”Enter step size: \n”;
cin>>step;

n= ceil((b-a)/step);
for (int k=0; k<=n-1; k++)
{
Left = a + k*step;
If (k == n-1)
{
Right=b;
}
}
Else
{
right=left+step;
}
Check_roots(left,right,a0,a1,a2,a3);
}
Check_roots(b,b,a0,a1,a2,a3);
Return 0;
}
New Function
Void check_roots(double left, double right, doubl a0, double a1, double a2, double a3)
{
Double f_left, f_right;
F_left = poly(left,a0,a1,a2,a3);
F_right=poly(right,a0,a1,a2,a3);
If (fabs(f_left) < 0.1e-04)
{
Cout<< “root detected at “ << left << endl;
}
If (fabs(f_right)<0.1e-04)
;
Else
{
If (f_left*f_right <0)
{
Cout<<”root detected at “<< (left+right)/2)<<endl;
}
}
}
Return;
}

New Function
Double poly(double x, double a0, double a1, double a2, double a3)
{
Return a0*x*x*x+a1*x*x+a2*x+a3;
}

[r035198x]

Where is the switch structure that was mentioned in your specs?
Better write the code (according to the specs) and post only if you get specific problems with it. Just dumping some pseudo code on us and asking us if it's correct is a no no.

[GolfinRover]

The descriminant value shows up but the roots do not output. Any thoughts?

Heres the problem specifications.

Function poly(given x, z, a, b, c; returns y)

Function roots(given degree, left, right, z, a, b, c, &secondRoot; returns estimateOfRoot)

Note: The roots function has a switch structure to process either a polynomial of degree 2 or 3 with case 2: to handle quadratic formula that returns two roots, one through the normal return statement via estimateOfRoot and a second root through the reference parameter &secondRoot; and with case 3: to handle the cubic polynomial with the incremental search technique.

Your main module should drive the roots function with PIE from the user for degree, coefficients, interval limits, and step size until the user decides to quit the program with a value of -1 for degree, that is, an input sentinel of -1 to terminate a loop in the main module that drives your Polynomial Roots Problem.

#include "head.h"
int main()
{//start main
    double a = 0, b = 0, c = 0, z = 0, stepsize = 0, leftbound = 0, rightbound = 0, secondroot = 0, root = 0;
    int degree = -1;
    cout << "Enter the desired degree(2 or 3) or type (-1) to quit: ";
    cin >> degree;
 
    while(degree != -1)
    {
        while((degree != 2) && (degree != 3))
        {
            cout << "\nThis is not an option." << endl;
            cout << "Enter the desired degree (2 or 3): ";
            cin >> degree;
        }
            cout << "\nEnter a, b, c, and z: ";
            cin >> a;
            cin >> b;
            cin >> c;
            cin >> z;
 
            if(degree == 3)
            {
 
                cout << "\nPlease enter the step size, right bound, and left bound: ";
                cin >> stepsize;
                cin >> rightbound;
                cin >> leftbound;
            }
 
            root = roots(degree, leftbound, rightbound, stepsize, z, a, b, c, secondroot);
 
            if (degree == 2)
            {//start if
                if (root != -9999)
                {//start inner if
                    cout << "Root 1 is: " << root << endl;
                    cout << "Root 2 is: " << secondroot << endl;
                }//end inner if
                else
                {//start else
                    cout << "Root 1 is an imaginary and can not be calculated" << endl;
                    cout << "Root 2 is an imaginary and can not be calculated" << endl;
                }//end else
            }// end if
 
            cout << "\nEnter the desired degree (2 or 3) or type (-1) to quit: ";
            cin >> degree;
 
    }//end while
}// end main
 
 
Poly.cpp FUNCTION
double poly(double x, double z, double a, double b, double c) 
 
{//start poly 
 
double y; 
 
y=z*pow(x,3)+a*pow(x,2)+b*x+c; 
 
return y; 
 
}//end poly
 
 
 
 
Roots.cpp FUNCTION
double roots(int degree, double leftbound, double rightbound, double stepsize, double z, double a, double b, double c, double &secondRoot)
{//start root
    double i = leftbound, test1 = 0, test2 = 0, root = 0, descrim = 0, estimateOfRoot = 0, rootnum = 0;
 
    switch(degree) 
    {//start switch
        case 2:
            // aX^2 + bX + c
            descrim = pow(-b,2) - 4 * a* c;
            cout << "The Descriminant is: " << descrim << endl;
            if(descrim < 0)
            {//start if
 
                estimateOfRoot = -9999;
                secondRoot = -9999;
            }// end if
            else
            {//start else
 
                estimateOfRoot = ((-b + sqrt(pow(-b,2) - 4 * a* c))/ (2*a));
                secondRoot = ((-b - sqrt(pow(-b,2) - 4 * a* c))/ (2*a));
            }//end else
 
            return estimateOfRoot;    
 
            break;
 
        case 3:
 
            descrim = pow(-b,2) - 4 * a* c;
            cout << "\nThe Descriminant is: " << descrim << endl;
            while(i < rightbound)
            {// start while
                test1 = poly(i, z, a, b, c);
                test2 = poly(i + stepsize, z, a, b, c);
 
                if(abs(test1) < 0.0001)
                {//start if
 
                    root = i;
                    cout << "There is a root at: " << root << endl;
                    rootnum++;
                }// end if
                else if((test1 * test2) < 0)
                {// start else
 
                    root = ((i + stepsize) + i) / 2;
                    cout << "There is a root at: " << root << endl;
                    rootnum++;
                }//end else
 
                i += stepsize;
            }// end while
    }
}

[arnaudk]

The descriminant value shows up but the roots do not output. Any thoughts?

Yes. Debug your code. Why don't you cout << root straight after

root = roots(degree, leftbound, rightbound, stepsize, z, a, b, c, secondroot);

to see what comes out? If the roots dont show then what happens instead? Does your program crash? Did you print out intermediate variables in your function like a,b,c to see they are what you expected? By the way, if degree==3 then the way you've written it you will never see your roots.

Please Use CODE tags around your code.