Logarithmic functions

[dbauer-ets]

@PhilippImhof

The ISO 80000-2 standard recommends that:

log_10(x) should be written lg(x)
log_e(x) should be written ln(x)
log_2(x) should be written lb(x)

I saw that you have added the ln() and lg() functions, which is great!

So now we have in the Formulas questions:

For the teacher:

log_10(x) → lg(x) and log10(x)
log_e(x) → ln(x) and log(x) :
Note that log() function can also be used with two arguments: log_a(x) → log(x,a)

For the student:

log_10(x) → lg(x) and log10(x)
log_e(x) → ln(x)
log(x) does not seem to work, which I think is ok because, as ISO pointed out, it can be confusing.
log(x,b) is not available because it is a two argument function, so this is ok at least for now.

My questions:

1. I am updating the documentation. Can you tell me if all of the above is correct?

2. Are there other functions that have been added to the question, so I can include them in the documentation?

3. I think that log_2(x) → lb(x) could eventually be added. What do you think?

[PhilippImhof]

Dear Dominique

Yes, you are right with everything. I have added 'lg' in #188. The function 'log' is not made available to students for two reasons: the single-argument form is ambiguous (some might write log and mean the common logarithm, although the LaTeX rendering that I am currently implementing would make that clear) and the two-argument form, well, is not because of the two arguments.

I will add lb as well; I thought of it, but was not sure whether it was worth it.

And I will send you a mail with all changes in detail so you don't have to look them up individually in order to update the docs.

[dbauer-ets]

Hello Philipp,

log10() used to work in previous versions, but it doesn’t seem to anymore.

Could you please confirm whether log10() is no longer supported?

[PhilippImhof]

Hello @dbauer-ets

I am pretty sure that log10 still works, because there are automated tests that explicitly check this function.

What problem do you have? I am more than happy to manually test it.

Best regards

[PhilippImhof]

@dbauer-ets I have just made a manual test and can see no problem with the log10 function. I am closing this; maybe you can open a new bug report with a specific case so I can investigate?

[dbauer-ets]

Hello Philipp,

In previous versions of the Formulas question type, log10(0) was not flagged as being undefined, so I hadn’t noticed my programming error, which, although harmless in my question, was still a mistake.

The new versions of the Formulas question type now correctly indicate that log10(0) is undefined. This is excellent and once again demonstrates the high quality of your work.

[PhilippImhof]

I think this can be closed now, especially because there is now a separate issue about the question whether or not INF and -INF should be flagged as errors.