Metodo de la biseccion en matlab con ingreso de funcion normal y syms (simbólico)

https://beastieux.com/2008/10/25/codigo-matlab-%E2%80%93-metodo-de-la-biseccion/

xai=input('Ingrese el intervalo inferior: ');

xbi=input('Ingrese el intervalo superior: ');

tol=input('Ingrese el porcentaje de error: ');

syms x;

f=input('Ingrese la funciòn: ');

i=1;

f1=subs(f,x,xai);

f2=subs(f,x,xbi);

ea(i)=100;

if f1*f2 < 0

    xa(i)=xai; f1=subs(f,x,xa(i));

    xb(i)=xbi; f2=subs(f,x,xb(i));

    xr(i)=(xa(i)+xb(i))/2; f3=subs(f,x,xr(i));

     

    fprintf('It.       Xa               Xr             Xb           Error aprox \n');

    fprintf('%2d \t %11.7f \t %11.7f \t %11.7f \n',i,xa(i),xr(i),xb(i));

    while abs(ea(i)) >= tol,

      if f1*f3<0

         xa(i+1)=xa(i);f1=subs(f,x,xa(i+1));

         xb(i+1)=xr(i);f2=subs(f,x,xb(i+1));

      end

      if f1*f3> 0

         xa(i+1)=xr(i);f1=subs(f,x,xa(i+1));

         xb(i+1)=xb(i);f2=subs(f,x,xb(i+1));

      end     

      xr(i+1)=(xa(i+1)+xb(i+1))/2; f3=subs(f,x,xr(i+1));

      ea(i+1)=abs((xr(i+1)-xr(i))/(xr(i+1))*100);

      fprintf('%2d \t %11.7f \t %11.7f \t %11.7f \t %7.3f \n',...

              i+1,xa(i+1),xr(i+1),xb(i+1),ea(i+1));

      i=i+1;

   end

else

   fprintf('No existe una raíz en ese intervalo');

end