BLD-434: Add fix for negative exponents.

Set default tolerance to 1e-3% for all responsetypes.

CHANGELOG.rst

@@ -5,6 +5,8 @@ These are notable changes in edx-platform.  This is a rolling list of changes,
 in roughly chronological order, most recent first.  Add your entries at or near
 the top.  Include a label indicating the component affected.
 
+Blades: Fix comparison of float numbers. BLD-434.
+
 Blades: Allow regexp strings as the correct answer to a string response question. BLD-475.
 
 Common: Add feature flags to allow developer use of pure XBlocks

common/lib/capa/capa/responsetypes.py

@@ -35,7 +35,8 @@ from calc import evaluator, UndefinedVariable
 from . import correctmap
 from datetime import datetime
 from pytz import UTC
-from .util import compare_with_tolerance, contextualize_text, convert_files_to_filenames, is_list_of_files, find_with_default
+from .util import (compare_with_tolerance, contextualize_text,  convert_files_to_filenames,
+                           is_list_of_files, find_with_default, default_tolerance)
 from lxml import etree
 from lxml.html.soupparser import fromstring as fromstring_bs     # uses Beautiful Soup!!! FIXME?
 import capa.xqueue_interface as xqueue_interface
@@ -832,7 +833,7 @@ class NumericalResponse(LoncapaResponse):
 
     def __init__(self, *args, **kwargs):
         self.correct_answer = ''
-        self.tolerance = '0'  # Default value
+        self.tolerance = default_tolerance
         super(NumericalResponse, self).__init__(*args, **kwargs)
 
     def setup_response(self):
@@ -1877,7 +1878,7 @@ class FormulaResponse(LoncapaResponse):
     def __init__(self, *args, **kwargs):
         self.correct_answer = ''
         self.samples = ''
-        self.tolerance = '1e-5'  # Default value
+        self.tolerance = default_tolerance
         self.case_sensitive = False
         super(FormulaResponse, self).__init__(*args, **kwargs)
 
@@ -2433,7 +2434,7 @@ class ChoiceTextResponse(LoncapaResponse):
                 input_name = child.get('name')
                 # Contextualize the tolerance to value.
                 tolerance = contextualize_text(
-                    child.get('tolerance', '0'),
+                    child.get('tolerance', default_tolerance),
                     context
                 )
                 # Add the answer and tolerance information for the current
@@ -2662,7 +2663,7 @@ class ChoiceTextResponse(LoncapaResponse):
 
             correct_ans = params['answer']
             # Set the tolerance to '0' if it was not specified in the xml
-            tolerance = params.get('tolerance', '0')
+            tolerance = params.get('tolerance', default_tolerance)
             # Make sure that the staff answer is a valid number
             try:
                 correct_ans = complex(correct_ans)

common/lib/capa/capa/tests/response_xml_factory.py

@@ -182,7 +182,10 @@ class NumericalResponseXMLFactory(ResponseXMLFactory):
         response_element = etree.Element('numericalresponse')
 
         if answer:
-            response_element.set('answer', str(answer))
+            if isinstance(answer, float):
+                response_element.set('answer', repr(answer))
+            else:
+                response_element.set('answer', str(answer))
 
         if tolerance:
             responseparam_element = etree.SubElement(response_element, 'responseparam')

common/lib/capa/capa/tests/test_responsetypes.py

@@ -56,13 +56,11 @@ class ResponseTest(unittest.TestCase):
     def assert_multiple_grade(self, problem, correct_answers, incorrect_answers):
         for input_str in correct_answers:
             result = problem.grade_answers({'1_2_1': input_str}).get_correctness('1_2_1')
-            self.assertEqual(result, 'correct',
-                             msg="%s should be marked correct" % str(input_str))
+            self.assertEqual(result, 'correct')
 
         for input_str in incorrect_answers:
             result = problem.grade_answers({'1_2_1': input_str}).get_correctness('1_2_1')
-            self.assertEqual(result, 'incorrect',
-                             msg="%s should be marked incorrect" % str(input_str))
+            self.assertEqual(result, 'incorrect')
 
     def _get_random_number_code(self):
         """Returns code to be used to generate a random result."""
@@ -1070,6 +1068,27 @@ class NumericalResponseTest(ResponseTest):
         incorrect_responses = ["", "4.5", "3.5", "0"]
         self.assert_multiple_grade(problem, correct_responses, incorrect_responses)
 
+    def test_floats(self):
+        """
+        Default tolerance for all responsetypes is 1e-3%.
+        """
+        problem_setup = [
+          #[given_asnwer, [list of correct responses], [list of incorrect responses]]
+            [1, ["1"], ["1.1"],],
+            [2.0, ["2.0"], ["1.0"],],
+            [4, ["4.0", "4.00004"],  ["4.00005"]],
+            [0.00016, ["1.6*10^-4"], [""]],
+            [0.000016, ["1.6*10^-5"], ["0.000165"]],
+            [1.9e24, ["1.9*10^24"], ["1.9001*10^24"]],
+            [2e-15, ["2*10^-15"], [""]],
+            [3141592653589793238., ["3141592653589793115."], [""]],
+            [0.1234567,  ["0.123456", "0.1234561"], ["0.123451"]],
+            [1e-5,  ["1e-5", "1.0e-5"], ["-1e-5", "2*1e-5"]],
+        ]
+        for given_answer, correct_responses, incorrect_responses in problem_setup:
+            problem = self.build_problem(answer=given_answer)
+            self.assert_multiple_grade(problem, correct_responses, incorrect_responses)
+
     def test_grade_with_script(self):
         script_text = "computed_response = math.sqrt(4)"
         problem = self.build_problem(answer="$computed_response", script=script_text)

common/lib/capa/capa/util.py

@@ -4,16 +4,28 @@ from cmath import isinf
 #-----------------------------------------------------------------------------
 #
 # Utility functions used in CAPA responsetypes
+default_tolerance = '0.001%'
 
 
-def compare_with_tolerance(v1, v2, tol):
-    ''' Compare v1 to v2 with maximum tolerance tol
+def compare_with_tolerance(v1, v2, tol=default_tolerance):
+    '''
+    Compare v1 to v2 with maximum tolerance tol.
+
     tol is relative if it ends in %; otherwise, it is absolute
 
-     - v1    :  student result (number)
-     - v2    :  instructor result (number)
+     - v1    :  student result (float complex number)
+     - v2    :  instructor result (float complex number)
      - tol   :  tolerance (string representing a number)
 
+     Default tolerance of 1e-3% is added to compare two floats for near-equality
+     (to handle machine representation errors).
+     It is relative, as the acceptable difference between two floats depends on the magnitude of the floats.
+     (http://randomascii.wordpress.com/2012/02/25/comparing-floating-point-numbers-2012-edition/)
+     Examples:
+        In [183]: 0.000016 - 1.6*10**-5
+        Out[183]: -3.3881317890172014e-21
+        In [212]: 1.9e24 - 1.9*10**24
+        Out[212]: 268435456.0
     '''
     relative = tol.endswith('%')
     if relative:
@@ -28,6 +40,8 @@ def compare_with_tolerance(v1, v2, tol):
         # `inf <= inf` which is a fail. Instead, compare directly.
         return v1 == v2
     else:
+        # v1 and v2 are, in general, complex numbers:
+        # there are some notes about backward compatibility issue: see responsetypes.get_staff_ans()).
         return abs(v1 - v2) <= tolerance
 
 

common/lib/xmodule/xmodule/js/src/problem/edit.coffee

@@ -3,7 +3,7 @@ class @MarkdownEditingDescriptor extends XModule.Descriptor
   @multipleChoiceTemplate : "( ) incorrect\n( ) incorrect\n(x) correct\n"
   @checkboxChoiceTemplate: "[x] correct\n[ ] incorrect\n[x] correct\n"
   @stringInputTemplate: "= answer\n"
-  @numberInputTemplate: "= answer +- x%\n"
+  @numberInputTemplate: "= answer +- 0.001%\n"
   @selectTemplate: "[[incorrect, (correct), incorrect]]\n"
   @headerTemplate: "Header\n=====\n"
   @explanationTemplate: "[explanation]\nShort explanation\n[explanation]\n"