Aproximate roots using Bairstow method

Hello guys.

I have a code in c++, which implement the Bairstow method, but I don't know how to convert it in Matlab.

Can anyone help me with some tips ? I know it is a code on this webside, which makes the same thing, but I don't understand it very well.

This is the code :

#include <iostream>

#include <math.h>

#include <stdlib.h>

using namespace std;

double a[100], p0, q0, b[100], c[100], delta, P, Q, R, S, eps;

int n, i;

double max(double a, double b) {

if (a >= b)

return a;

else

return b;

}

void rezolv_ec2(double a, double b, double c) {

double d, x1, x2;

d = b * b - 4 * a*c;

if (d >= 0) {

cout << "\n" << (-b - sqrt(d)) / (2 - a) << endl;

cout << "\n" << (-b + sqrt(d)) / (2 - a) << endl;

}

if (d < 0) {

cout << "\n" << -b / (2 * a) << "-i*" << sqrt(-d) / (2 * a);

cout << "\n" << -b / (2 * a) << "+i*" << sqrt(-d) / (2 * a);

}

}

void rezolv_ec1(double a, double b) {

cout << "\n" << -b / a << endl;

}

void main() {

cout << "Dati gradul ec.="; cin >> n;

for (i = 0; i <= n; i++) {

cout << "a[" << i << "]="; cin >> a[i];

}

do {

cout << "\np0="; cin >> p0;

cout << "\nq0="; cin >> q0;

cout << "\nDati eroarea admisa eps="; cin >> eps;

do {

b[0] = a[0];

b[1] = a[1] - p0 * b[0];

for (i = 2; i <= n; i++) {

b[i] = a[i] - p0 * b[i - 1] - q0 * b[i - 2];

}

c[0] = b[0];

c[1] = b[1] - p0 * c[0];

for (i = 2; i <= n - 1; i++) {

c[i] = b[i] - p0 * c[i - 1] - q0 * c[i - 2];

}

delta = pow(c[n - 2], 2) - c[n - 3] * c[n - 1] + c[n - 3] * b[n - 1];

P = -b[n - 1] * c[n - 2] + b[n] * c[n - 3];

Q = -b[n] * c[n - 2] + b[n - 1] * c[n - 1] - pow(b[n - 1], 2);

p0 -= P / delta;

q0 -= Q / delta;

R = b[n - 1];

S = b[n] + p0 * b[n - 1];

} while (max(fabs(R), fabs(S)) > eps);

cout << "\nRadacinile ecuatiei sunt:";

rezolv_ec2(1, p0, q0);

n = n - 2;

for (i = 0; i <= n; i++) {

a[i] = b[i];

}

} while (n >= 3);

if (n == 2)

rezolv_ec2(b[0], b[1], b[2]);

if (n == 1)

rezolv_ec1(b[0], b[1]);

}

Answer 1

[Sai Sri Pathuri]

You may use the following resources

1. Declare function name, inputs, and outputs - https://in.mathworks.com/help/matlab/ref/function.html
2. if, elseif, else Documentation - https://in.mathworks.com/help/matlab/ref/if.html
3. Display text in the Command Window - disp or fprintf
4. Loops - for and while
5. Do while loop in MATLAB - https://in.mathworks.com/matlabcentral/answers/115403-do-while-loop-in-matlab#answer_123751