Método de la Bisección en Matlab

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