Why the 'bisect' in my coding is undefined?

Hereby, this is my coding and the question is attached below.

Q=20;
g=9.81;
B=@(y)3+y;
Ac=@(y)3*y+y.^2/2;
func=@(y)(1-Q^2*B(y)./(g*Ac(y).^3));
xu=2.5;
xl=0.5;
es=0.01;
n_iter=10;

%%graphically
x=0.5:0.1:2.5;
plot(x,func(x),'r',x,0.*x,'b--');

%%numerically
[root1, f_1, e_1, n_1] = bisect(func,xl,xu,es,n_iter);
[root_2,f_2,e_2,n_2]=false_position(func,xl,xu,es,n_iter);

fprintf('Bisection method: \n');
fprintf('\t root:%g\n',root_1);
fprintf('\t function value at root:%g\n',f_1);
fprintf('\t approximate relative error:%g\n',e_1);
fprintf('\t number of iterations:%d\n\n',n_1);

fprintf('Bisection method: \n');
fprintf('\t root:%g\n',root_2);
fprintf('\t function value at root:%g\n',f_2);
fprintf('\t approximate relative error:%g\n',e_2);

fprintf('\t number of iterations:%d\n\n',n_2);

[dpb]

There's no bisect function here; you must create the bisect.m file and have it someplace on the MATLABPATH to be found.

[Thirunaukkarasu Asogan]

I did that and i obtained "invalid call to script'.

[John D'Errico]

Then it looks as if you have not defined a function named bisect, but a script file. Time to learn what a function is and how to write one?

[Thirunaukkarasu Asogan]

yes maybe you can assist me with that.

[dpb]

Start by typing

doc function

and follow along...