Método de la Regla Falsa en Matlab

xai=input('Ingrese limite inferior: ');
 xbi=input('Ingrese limite superior: ');
  tol=input('Ingrese el porcentaje de Error: ');
   syms x;
    f=input('Ingrese la Funcion: ');
     f1=subs(f,x,xai);
   f2=subs(f,x,xbi);
  i=1;
 ea(1)=100;
if f1*f2 < 0
    xa(1)=xai;f1=subs(f,x,xa(1));
     xb(1)=xbi;f2=subs(f,x,xb(1));
     xr(1)=xa(1)-f1*(xb(1)-xa(1))/(f2-f1); f3=subs(f,x,xr(1));
      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(1)=xr(i);
         xb(1)=xb(i);
      end
        xr(i+1)=xa(i+1)-f1*(xb(i+1)-xa(i+1))/(f2-f1);
         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