Calculating More Trigonometric Functions
Problem
You want to calculate values for trigonometric functions like sine, tangent, or arc-cosine.
Solution
Perl provides only
sin
, cos
, and
atan2
as standard functions. From these, you can
derive tan
and the other trig functions:
sub tan { my $theta = shift; return sin($theta)/cos($theta); }
The POSIX module provides a wider range of trig functions:
use POSIX; $y = acos(3.7);
The Math::Trig module provides a complete set of functions and supports operations on or resulting in complex numbers:
use Math::Trig; $y = acos(3.7);
Discussion
The tan
function will cause a
division-by-zero exception when $theta
is
,
, and so on, because the
cosine is for these values. Similarly, tan
and many
other functions from Math::Trig may generate the same error. To trap
these, use eval
:
eval { $y = tan($pi/2); } or return undef;
See Also
The sin
, cos
, and
atan2
functions in perlfunc
(1) and Chapter 3 of Programming Perl; we
talk about trigonometry in the context of imaginary numbers in Section 2.15; we talk about the use of
eval
to catch exceptions in Section 10.12
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