Dr. David Kirkby

One of the staff tutors at the Open University contacted me with a simpler example. I'll just copy/paste what he wrote: "If you would like to see an easier example of the carg bug then it happens for any angle larger than pi/2. For example trigreduce(carg(cos(3%pi/5)+%i * sin(3%pi/5))) will give the incorrect answer."

I've asked a few people at the Open University if they know of a simpler example. None do, but one of the senior academics is going to try to look into whether she can provide a simpler example. I don't have the mathematical ability to do so myself, but I knew enough of Mathematica to satisfy myself they were correct in identifying this as a bug.

Something has probably changed in trigreduce then, as it used to work properly. I did not add any labels to this bug report - I did not see the option. But perhaps someone with more knowledge of me can add appropriate labels. It's impressive how nice the result is from earlier versions of Maxima compare to a current version of Mathematica, which produces a huge expression, rather than a simple irrational number. But Maxima producing the wrong answer is clearly not desirable.

I should have added, the result from the earlier version of Maxima for trigreduce(carg(c/d)) is 24 Pi/13. Is you subtract 2 Pi it is -2 Pi/13, which is what Mathematica gives, with N[TrigReduce[Arg[c/d]], 60] -0.483321946706122036686560520504538905261102984519247049380761 N[-2 Pi/13, 60] -0.483321946706122036686560520504538905261102984519247049380761

Results computed with Mathematica.

Maxima worksheet demonstrating the bug.

Adding a section from the Open University Computer Algebra guide for the module I'm studying.

Error with complex numbers - example with trigreduce