clc
f1=@(x) exp(-x)-x;

function yy=FalsePos(f,xl,xu,es,imax,xr,iter,ea)
  iter=0;
  fl=f(xl);
  while or((ea<es),(iter<=imax))
     xrold=xr;
     xr=xu-(f(xu)*(xl-xu))/(f(xl)-f(xu));
     fr=f(xr);
     iter=iter+1;
     if ne(ea,0)
       ea=abs((xr-xrold)/xr)*100;
     end
     test=fl*fr;
     if (test<0)
        xu=xr;
     elseif (test>0)
          xl=xr;
          fl=fr;
     else ea=0;
          break;
     end
  end
    yy=xr;
end

fplot(f1,[0 1],'b')
grid on;
#  (f,xl,xu,es,imax,xr,iter,ea)
r1=FalsePos(f1,0,1,3,2,0.25,0,2.6);
fprintf("El valor de la raiz es = %f \n",r1)