Fixed point iteration issue

Need help to find the error its not matlab its sagemath, i couldnt find any forum of sagemath that worked. would apreciate any help.

sage: def valores2(f,p,a,b,x,n): ... var('k,xk,fi(xk),Er.Abs,Er.Rel,Er.Met') ... x==x ... a == a ... b == b ... ... Z=[[k,xk,fi(xk),Er.Abs,Er.Rel,Er.Met]] ... for i in range (0,n): ... Z.append([i,x,p(x),ea,er,em]) ... ... if f(a)*f(b)<0: ... print("check") ... else: ... print("not check") ... ... ... ... er = abs(p(x)-x) ... ... if x > 1: ... ea = er/x ... else: ... ea = er ... ... ... df = diff(f,x) ... ... dp = diff(p,x) ... ... ... if df(x) > 0: ... l = abs(dp(b)) ... else: ... l = abs(dp(a)) ... ... em = ea*(l*(1-l)) ... ... ... x=p(x) ... ... ... return (matrix(Z)) sage: @interact sage: def Exp(n = selector(range(0, 11),nrows=1, label="Botão"),f = input_box(default=x*e^x -1), x = input_box(default=0.8), p = input_box(default=e^(-x)), a = input_box(default=0.5), b = input_box(default=1)): ... ... show(valores2(f,p,a,b,x,n))

#######----ERROR-----######

Traceback (most recent call last): File "<stdin>", line 1, in module File "_sage_input_5.py", line 10, in module exec compile(u'open("___code___.py","w").write("# -*- coding: utf-8 -*-\\n" + support.preparse_worksheet_cell(base64.b64decode("X2ludGVyYWN0Xy5yZWNv\ bXB1dGUoJzMxJyk="),globals())+"\\n"); execfile(os.path.abspath("___code___.py"))' + '\n', '', 'single') File "", line 1, in module

File "/tmp/tmp4lQStw/___code___.py", line 2, in <module>
  exec compile(u"_interact_.recompute('31')" + '\n', '', 'single')
File "", line 1, in <module>

File
"/home/sage/sage-6.3/local/lib/python2.7/site-packages/sagenb-0.10.8.2-p\
y2.7.egg/sagenb/notebook/interact.py", line 3892, in recompute
  S['function']()
File
"/home/sage/sage-6.3/local/lib/python2.7/site-packages/sagenb-0.10.8.2-p\
y2.7.egg/sagenb/notebook/interact.py", line 2674, in _
  z = f(*[variables[arg] for arg in args])
File "/tmp/tmpySnhLB/___code___.py", line 6, in Exp
  show(valores2(f,p,a,b,x,n))
File "/tmp/tmpNEoaxc/___code___.py", line 4, in valores2
  var('k,xk,fi(xk),Er.Abs,Er.Rel,Er.Met')
File "var.pyx", line 139, in sage.calculus.var.var
(build/cythonized/sage/calculus/var.c:1033)
File "ring.pyx", line 595, in sage.symbolic.ring.SymbolicRing.var
(build/cythonized/sage/symbolic/ring.cpp:7913)
File "ring.pyx", line 643, in sage.symbolic.ring.SymbolicRing.var
(build/cythonized/sage/symbolic/ring.cpp:7657)
ValueError: The name "fi(xk)" is not a valid Python identifier.