Trying to do bisection, new to MATLAB

My code is:

 function f = bisection2(g,a,b)
 g= @x 3*x - e^x
 while 1
    p =(a+b)/2;
    if p-a< 10^-5, break;end
    if g(a)*g(p)>0
        a = p;
    else
        b = p;
    end
  end %while 1

I have tried defining g in a separate .m file, but I keep getting an error in that line. 3x-e^x is the function I am trying to apply bisection to. I am using R2018b.

Answer 1

[ANKUR KUMAR]

As your equation negative value at both ends. So bisection can not be possible for your equation. I am giving this example by taking different function.

 g= @(x) 2*x + sin(x)
  bisection(g,-5,10)

function p = bisection(f,a,b)
f(a)
f(b)
if f(a)*f(b)>0
    disp('The function has positive value at the end points of interval.');
    disp('The root can''t be found using bisection method, use some other method.');
else
    p = (a + b)/2;
    err = abs(f(p));
    while err > 1e-7
        if f(a)*f(p)<0
            b = p;
        else
            a = p;
        end
        p = (a + b)/2;
        err = abs(f(p));
    end
end
end

References:

a) https://in.mathworks.com/matlabcentral/fileexchange/43535-bisection-m

b) https://in.mathworks.com/matlabcentral/fileexchange/33748-bisection-method

[James Cortez]

Figured out what I was doing wrong. I was trying to initiate g inside a .m file instead of putting

"g= @(x) 3*x - exp(x)" into the command window. Hopefully this will help someone else that is just starting out.