2.11. Calculating More Trigonometric Functions2.11.1. ProblemYou want to calculate values for trigonometric functions like sine, tangent, or arc-cosine. 2.11.2. SolutionPerl 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. DiscussionThe 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 AlsoThe 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 Copyright © 2003 O'Reilly & Associates. All rights reserved. |
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