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2.12. 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 Graphic, Graphic, 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;

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 Recipe 2.15; we talk about the use of eval to catch exceptions in Recipe 10.12


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