Moodle

Edge case missing from Calculated qtype

Details

  • Type: Bug Bug
  • Status: Closed Closed
  • Priority: Minor Minor
  • Resolution: Fixed
  • Affects Version/s: 2.0.4, 2.1.1, 2.2
  • Fix Version/s: 2.0.5, 2.1.2
  • Component/s: Questions
  • Labels:
  • Testing Instructions:
    Hide

    1. Start creating a new calculated question with all defaults, except:
    Name: <whatever>
    Answer Formula:

    {x}

    *1E-12
    Answer Grade: 100%
    Format: Significant Figures

    2. Click Save changes then Next page

    3. On this page set
    Range of Values: 1.0-1.1
    Decimal places: 1
    Then Add 30 new set(s) of wild card(s) values

    4. Verify that there are no errors like "ERROR Correct answer : 100e-13 outside limits of true value 1.0E-12"

    Show
    1. Start creating a new calculated question with all defaults, except: Name: <whatever> Answer Formula: {x} *1E-12 Answer Grade: 100% Format: Significant Figures 2. Click Save changes then Next page 3. On this page set Range of Values: 1.0-1.1 Decimal places: 1 Then Add 30 new set(s) of wild card(s) values 4. Verify that there are no errors like "ERROR Correct answer : 100e-13 outside limits of true value 1.0E-12"
  • Affected Branches:
    MOODLE_20_STABLE, MOODLE_21_STABLE, MOODLE_22_STABLE
  • Fixed Branches:
    MOODLE_20_STABLE, MOODLE_21_STABLE
  • Pull from Repository:
  • Pull Master Branch:
  • Pull Master Diff URL:

Description

When using the significant figures calculation mode, an edge case is not properly handled in the function 'qtype_calculated_calculate_answer', causing the calculated answer to be incorrect.

The function works to ensure the answer is expressed as a string of the format "0.[1-9][0-9]*", but subsequently calls the round() function. In some cases, round will round up to 1.0- which is no longer in the assumed format. This causes an answer to be produced which is exactly 10x larger than the correct answer.

A special case should be added to compensate, as in the attached patch.

Activity

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Tim Hunt added a comment -

Would be nice to see some additional unit tests to cover this case.

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Tim Hunt added a comment - Would be nice to see some additional unit tests to cover this case.
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Pierre Pichet added a comment -

Kim,
Have you a numerical example that we could use to test.
However these ronding effects are also related to the PHP precision settings.

Show
Pierre Pichet added a comment - Kim, Have you a numerical example that we could use to test. However these ronding effects are also related to the PHP precision settings.
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Kyle Temkin added a comment -

Try creating the following Simple Calculated Question:

All defaults, except:
Name: <whatever>
Answer Formula:

{x}E-12
Answer Grade: 100%
Format: Significant Figures

Wildcard range for {x}

: 1.0-1.1
Decimal places: 1

Then, generate any large amount of wildcards. I chose 30. I receive the following error on any wildcard generated with the value 1.0:

"ERROR Correct answer : 100e-13 outside limits of true value 1.0E-12"

Show
Kyle Temkin added a comment - Try creating the following Simple Calculated Question: All defaults, except: Name: <whatever> Answer Formula: {x}E-12 Answer Grade: 100% Format: Significant Figures Wildcard range for {x} : 1.0-1.1 Decimal places: 1 Then, generate any large amount of wildcards. I chose 30. I receive the following error on any wildcard generated with the value 1.0: "ERROR Correct answer : 100e-13 outside limits of true value 1.0E-12"
Hide
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Kyle Temkin added a comment -

The primary problem is a rounding issue- which is more common than you'd think, given the way floating point numbers are stored internally.

Here's the problem described and demonstrated in a simple PHP script:

http://labs.ktemkin.com/moodle/bugs/rounding.phps

You can execute it on my server here:
http://labs.ktemkin.com/moodle/bugs/rounding.php

And with the proposed patch:

http://labs.ktemkin.com/moodle/bugs/rounding_patched.phps
http://labs.ktemkin.com/moodle/bugs/rounding_patched.php

Let me know if you have any questions.

Show
Kyle Temkin added a comment - The primary problem is a rounding issue- which is more common than you'd think, given the way floating point numbers are stored internally. Here's the problem described and demonstrated in a simple PHP script: http://labs.ktemkin.com/moodle/bugs/rounding.phps You can execute it on my server here: http://labs.ktemkin.com/moodle/bugs/rounding.php And with the proposed patch: http://labs.ktemkin.com/moodle/bugs/rounding_patched.phps http://labs.ktemkin.com/moodle/bugs/rounding_patched.php Let me know if you have any questions.
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Pierre Pichet added a comment -

Thanks Kim,

Things are ever more complex as PHP being an interpreted language that can tolerate such an expression as

{x}E-12.

look at the following case


 {x}

E-12 1.0E-12 = 10000e-13
Min: 9.8999999999999E-13---Max: 1.01E-12
Erreur de réponse correcte : 10000e-13 en dehors des limites de la valeur réelle 1.0E-12
 
This was from UQAM (my university) 1,9 site with calculated question.
This part of the code can be trace back to older version.

How do I got 10000e-13.

This was by setting the answer with 4 significant figures.

As long as the x is 1.0 (i.e. 1.000 ) all the expression is not correctly handled.
If the value is different as 1.00001 things are OK.

The only computer I have access (holidays...) is an Ipad .

Could you test if your patch applied to moodle code also corrected this bad rounding effect.
 

Show
Pierre Pichet added a comment - Thanks Kim, Things are ever more complex as PHP being an interpreted language that can tolerate such an expression as {x}E-12. look at the following case  {x} E-12 1.0E-12 = 10000e-13 Min: 9.8999999999999E-13---Max: 1.01E-12 Erreur de réponse correcte : 10000e-13 en dehors des limites de la valeur réelle 1.0E-12   This was from UQAM (my university) 1,9 site with calculated question. This part of the code can be trace back to older version. How do I got 10000e-13. This was by setting the answer with 4 significant figures. As long as the x is 1.0 (i.e. 1.000 ) all the expression is not correctly handled. If the value is different as 1.00001 things are OK. The only computer I have access (holidays...) is an Ipad . Could you test if your patch applied to moodle code also corrected this bad rounding effect.  
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Pierre Pichet added a comment -

As a reminder, I also noticed that the left unit option is not handled correctly.

if (1 == $answerlength)

{ $calculated->answer = $sign.$answer.$exponent.$unit; }

else {
// Attach additional zeros at the end of $answer,

Show
Pierre Pichet added a comment - As a reminder, I also noticed that the left unit option is not handled correctly. if (1 == $answerlength) { $calculated->answer = $sign.$answer.$exponent.$unit; } else { // Attach additional zeros at the end of $answer,
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Tim Hunt added a comment -

Pierre, I think Kyle's fix is good, so submitting it for integration.

You are right that unit handling is wrong here, but I think we should handle that as a separate issue.

By the way, a formula like

{x}E-12 does not work when it comes to attempting the question. It needs to be written as {x}

*1E-12, which seems far more sensible to me anyway.

Show
Tim Hunt added a comment - Pierre, I think Kyle's fix is good, so submitting it for integration. You are right that unit handling is wrong here, but I think we should handle that as a separate issue. By the way, a formula like {x}E-12 does not work when it comes to attempting the question. It needs to be written as {x} *1E-12, which seems far more sensible to me anyway.
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Pierre Pichet added a comment -

By the way, a formula like

{x}E-12 COULD work when it comes to attempting the question.
The {x}

will be converted to the numerical to which the exponent will be applied as E number style is allowed in PHP
2.4E3 = 2400
I use this here to test the conversion process as any operation (ie.

{x}

*1E-12 ) could interfere with what we need to test.

P.S. even generating a number as large as in 1E45 range give a valid result.
992964467961790114603370108662767761814978560.0E3 = 9.9e47
PHP math functions seem quite robust..

Show
Pierre Pichet added a comment - By the way, a formula like {x}E-12 COULD work when it comes to attempting the question. The {x} will be converted to the numerical to which the exponent will be applied as E number style is allowed in PHP 2.4E3 = 2400 I use this here to test the conversion process as any operation (ie. {x} *1E-12 ) could interfere with what we need to test. P.S. even generating a number as large as in 1E45 range give a valid result. 992964467961790114603370108662767761814978560.0E3 = 9.9e47 PHP math functions seem quite robust..
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Eloy Lafuente (stronk7) added a comment -

Integrated (blind mode). Thanks!

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Eloy Lafuente (stronk7) added a comment - Integrated (blind mode). Thanks!
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Sam Hemelryk added a comment -

Tested. Passed. Thanks

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Sam Hemelryk added a comment - Tested. Passed. Thanks
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Aparup Banerjee added a comment -

fixes have been rolled merrily up the stream! Thanks everybody!

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Aparup Banerjee added a comment - fixes have been rolled merrily up the stream! Thanks everybody!

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Dates

  • Created:
    Updated:
    Resolved: