[metapost] Metafun : is "atan" the arctangent function?
Daniel H. Luecking
luecking at uark.edu
Sun Jan 12 20:02:31 CET 2014
On Jan 12, 2014, at 9:32am, jkitzm wrote:
>atan is vardef'd in mp-tool.mpiv as: x-(x**3)/3+(x**5)/5-(x**7)/7 ,
>part of the infinite series form. Maybe better to use asin(a/sqrt(a**2+1))?
The functions asin and acos are similarly defined in mp-tool:
vardef asin primary x = (x+(x**3)/6+3(x**5)/40) enddef ;
vardef acos primary x = (asin(-x)) enddef ;
(That second one is just wrong, it should be (90-asin(x)).)
But those functions are redefined a few lines later using "angle":
vardef asin primary x = angle((1+-+x,x)) enddef ;
vardef acos primary x = angle((x,1+-+x)) enddef ;
It is unclear why only atan was left with its bad definition.
This is clearly a bug.
Note that the asin and acos functions return degrees. The file
mp-tool.mpiv also also defines the alternatives invsin and
invcos, which return radians.
Regards,
Dan
--
Daniel H. Luecking
Department of Mathematical Sciences
University of Arkansas
Fayetteville, Arkansas
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