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2.11. Calculating More Trigonometric Functions
2.11.1. Problem
You want to calculate values for trigonometric functions like sine, tangent, or arc-cosine.
2.11.2. Solution
Perl provides only sin, cos, and atan2 as standard functions. From these, you can derive tan and all other trig functions (if you're intimately familiar with esoteric trig identities):
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 standard 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);
2.11.3. Discussion
The tan function will cause a division-by-zero exception when $theta is π/2, 3π/2, and so on, because the cosine is 0 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;2.11.4. See Also
The sin, cos, and atan2 functions in perlfunc(1) and Chapter 29 of Programming Perl; the documentation for the standard Math::Trig module; we talk about trigonometry in the context of imaginary numbers in Recipe 2.14; we talk about the use of eval to catch exceptions in Recipe 10.12
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| 2.10. Doing Trigonometry in Degrees, Not Radians |  | 2.12. Taking Logarithms |
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