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From: Lawrence D'Oliveiro <ldo@nz.invalid>
Newsgroups: comp.lang.fortran
Subject: Angle Units For Trig Functions
Date: Sun, 20 Oct 2024 03:47:13 -0000 (UTC)
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I see that the Fortran 2023 spec has added a bunch of parallel trig 
functions that work in degrees.

I find this sort of thing unnecessary. It seems conventional to add 
functions for converting between degrees and radians, but a simpler way is 
to simply define a conversion factor for each angle unit. One conversion 
factor is simpler than two functions for each angle unit.

So trig functions always work in radians. Supposing we have

    real, parameter :: DEG = PI / 180
    real, parameter :: CIRCLE = 2 * PI
    real, parameter :: RAD = 1

Then

    sin(x) -- sin of x in radians
    sin(x * DEG) -- x is in degrees
    atan2(y, x) -- arctangent is in radians
    atan2(y, x) / DEG -- arctangent is in degrees

and we can furthermore have equivalences like

    sin(90 * DEG) = sin(0.25 * CIRCLE) = sin(PI / 2)

(to within rounding error, of course)

and it is easy enough to add other units, e.g.

    real, parameter :: GRAD = PI / 200

Anybody remember those?