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List:       lon-capa-cvs
Subject:    [LON-CAPA-cvs] cvs: doc /help/developers LC2_student_equation_syntax.txt
From:       damieng <damieng () source ! lon-capa ! org>
Date:       2014-09-23 20:11:47
Message-ID: cvsdamieng1411503107 () cvsserver
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damieng		Tue Sep 23 20:11:47 2014 EDT

  Added files:                 
    /doc/help/developers	LC2_student_equation_syntax.txt 
  Log:
  added developers directory and a doc for student equation syntax
  
  

Index: doc/help/developers/LC2_student_equation_syntax.txt
+++ doc/help/developers/LC2_student_equation_syntax.txt
STUDENT EQUATION SYNTAX FOR MATHRESPONSE AND FORMULARESPONSE

* mathresponse or formularesponse with a CAS:

Note: by default, formularesponse uses Maxima. mathresponse requires the \
specification of the CAS.

Processing of the response:
1) separation of the string using the comma separator
2) addition of the implicit operators
  a b -> a*b
  3 b -> 3*b
  3 4 -> 3*4
  )( -> )*(
  ) ( -> )*(
  3a -> 3*a
  3( -> 3*(
  3 ( -> 3*(
  a ( -> a*(
  )a -> )*a
  )3 -> )*3
  ) 3 -> )*3
3) in the case of Maxima, tranformation of pi into %pi
4) run of the CAS with the script and the arguments
5) interpretation of the result: true -> EXACT_ANS, false -> INCORRECT, other -> \
BAD_FORMULA

Consequences:
- the general syntax is the one of the chosen CAS (Maxima or R), with implicit \
                operators
- students can use all the CAS functions in the active libraries, except the \
blacklisted ones and the ones using more than one argument. For instance, "mod(9,5)" \
will not work because the string is separated into 2 arguments. Some other important \
Maxima functions that cannot be used: diff, integrate, sum, product, limit, binomial, \
                atan2. With R %% can be used for the modulo.
- vectors can only be entered with a comma separated string which has then to be \
reconstructed with the arguments in the CAS script. A vector with the CAS syntax will \
                not be recognized.
- matrices cannot be entered
- with Maxima, constants such as inf, minf, und, %e, %i, %pi and pi are recognized. \
                Other constants than pi needing a percent sign, such as e and i, are \
                not recognized.
- R recognizes pi, Inf and NaN, but not i or e. Due to the preprocessing, complex \
                numbers cannot be entered.
- sometimes the result will be incorrect even though it's a syntax error (for \
instance when a function name is unknown with Maxima)


* formularesponse with samples:
- parenthesis
- implicit operator: *
- known operators: + - * / ^ % (modulo)
- known constants: only the ones that are explicitely used in the expected answer.
- some unknown operators: !
- known functions: abs, exp, log (log e), sqrt, factorial, sgn, ceil, floor, erf, \
                erfc, sin, cos, tan, asin, acos, atan, sinh, cosh, tanh, asin, acosh, \
                atanh
- some unknown functions: ln, log10, pow, atan2, min, max
Other functions that should not be used by students seem to be recognized, like \
duration() and problem(). It looks like functions with more than one argument (like \
pow) and functions with digits in the name (like log10) are not recognized, even \
though CAPA knows about them. Probably because of a preprocessing similar to the one \
used with CAS.


* Summary: common features (for formularesponse and mathresponse, Maxima, R or \
                samples):
- parenthesis
- implicit operator: *
- operators: + - * / ^
- functions: abs, exp, log (log e), sqrt, factorial, floor, sin, cos, tan, asin, \
                acos, atan, sinh, cosh, tanh, asin, acosh, atanh
- constants: pi, inf (assuming they are expected to be used when samples are used)


* Advice for authors
- Avoid asking students for expressions that require the use of a feature that does \
not work with all cases, such as constants other than pi. It makes it easier to \
switch later from CAS to samples or the other way around. It also keeps the syntax \
                compatible with other LON-CAPA problems.
- Add some problems at the beginning of the course to train students to the syntax. \
In particular, make sure they will not use an expression like "xy" to mean "x*y". For \
                example:
/res/msu/kortemey/physicsprecourse/inputpractice/algebraic.problem



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