# IRC log for #webwork, 2014-02-09

All times shown according to UTC.

Time Nick Message
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02:49 niall1 Any solution for the +-1f(x) formatting problem if the constant multiplying f(x) is negative or +-1?
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20:48 niall1 Webwork seems to be failing a lot when checking anti-derivatives that use logs
20:48 niall1 Is there a standard way of formatting the log function so that these mistakes are not made?
20:48 niall1 For instance, the system appears to detect that log(x) and log(abs(x)) are the same input
20:49 niall1 However, they are not taken to be the same when evaluated by the compare function
20:49 niall1 Hence the student will get a correct andwer for the second input log(abs(x)) but not log(x)
20:49 niall1 But the system will tell the students that the inputs are identical
20:52 niall1 Basically, it seems that webwork does not handle the logarithm function correctly
21:00 niall1 Trying to find solutions to problems like this is an infruiatingly frustrating expierience
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21:18 niall1 Basically, can webwork accept a function like log(2x+7) as an answer?
21:19 mgage yes
21:19 niall1 Consistently?
21:19 mgage yes -- it's very reliable
21:19 niall1 I'm trying to program the anti-derivative of 1/(Ax+B)
21:19 niall1 A and B are allowed to be negative
21:21 mgage in that case you might want to program your answer as log(abs(2x+7) or log(| 2x+7 |).  For the latter you will need to use MathObjects
21:21 niall1 Webwork checks the students answers verses log(abs(Ax+B))
21:21 mgage not the older answer checkers
21:21 niall1 But the problem is, when they input log|Ax+B| after log(Ax+B), if tells them that the second answer is equivilent to the first
21:22 mgage in that case specify the domain of points for checking the answer so that it will include both positive and negative entries.
21:23 niall1 I'll try using matheobjects instead
21:23 mgage probably the comparison points were chosen so that both log(ax+b) and Log (|ax+b|) were correct
21:24 mgage it probably won't make a big difference since MathObjects are used behind the scenes now in most of the old evaluation.  But you have more control if you work with MathObjects directly.
21:57 niall1 Can formulas simplify things like 2/4 when they appear? Is there a method to do this?
21:57 niall1 Which still leaving this rational I mean
21:57 niall1 In other words, coefficients like 2/4 are replaced by 1/2
21:58 mgage I don't think MathObjects will do that.  The command ->reduce() will take of things  like replacing 1x by 1  and x^1 by x  but not much more than that -- at least on a regular basis.
21:59 mgage There might be some tricks -- but for that I would ask on the forum and see what is suggested.  Davide Cervone might have some ideas
22:00 niall1 It's not vital at  the moment. Do you mean the main webwork forums?
22:04 niall1 Are all the reduction rules turned on by default, or do you need to turn on specific ones?
22:05 mgage I mean the main webwork forums (there is one devoted to authoring problems -- but it doesn't much matter where you ask).  I don't know which reduction rules are on my default.
22:06 mgage by default
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22:21 niall1 Oooo! MathObjects are smart.
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