How can I fix this? am trying to find the value of p with bisection method

syms p
x = 13.61015;
y = 13257;
a = 5.14;
b = 11.47;
c = 0;
f = (x^3 + p^2*x^2 - 10)*sin(x) == 0;
%eqn = y - (x^3 + p^2*x^2 - 10)*sin(x) == 0;
%p = vpasolve(eqn,p);
%p = p(p>a & p<b);
i=0;
while (x^3 + a^2*x^2 - 10)*sin(x) * (x^3 + b^2*x^2 - 10)*sin(x) > 0 && i<5 ;
    b = (a+b)/2;
    i=i+1;
end
disp (b);

[Jan]

If you ask for a fixing, it is useful to mention, which problem you have. It is easier to solve a problem than to guess, what the problem is.

The bisection method is a numerical approximation. Why do you choose a symbolic variable? You define f, but do not use it anywhere.

Search in the net for "bisection method". Look in Matlab's FileExchange. Your code has only some few similarities with it.

Answer 1

[Shubham Dhanda]

Hi,

I understand that you want to find the root of the equation f using bisection method.

To fix the code, define the value of p initially and then inside the while loop, calculate the value of p using the bisection method.

Below is the MATLAB code implementation of the problem:

syms p
x = 13.61015;
y = 13257;
a = 5.14;
b = 11.47;
c = 0;
i = 0;
p = (a + b)/2;

while abs(x^3 + p^2*x^2 - 10)*sin(x) > c && i < 5
    if (x^3 + a^2*x^2 - 10)*sin(x) * (x^3 + p^2*x^2 - 10)*sin(x) > 0 
        a = p;
    else
        b = p;
    end
    p = (a + b)/2;
    i = i + 1;
end

disp(p);

   11.3711

Attaching some links for your reference, these might help:

• bisection Method - Search - Help Center - MATLAB & Simulink (mathworks.com)
• Bisection Method Root Finding - File Exchange - MATLAB Central (mathworks.com)
• Bisection Method (bisection_method) - File Exchange - MATLAB Central (mathworks.com)