NAME

sin, cos, tan, asin, acos, atan, atan2 − trigonometric functions

SYNOPSIS

#include <math.h>

double sin(x)
double x;

double cos(x)
double x;

void sincos(x, s, c)
double x, ∗s, ∗c;

double tan(x)
double x;

double asin(x)
double x;

double acos(x)
double x;

double atan(x)
double x;

double atan2(y, x)
double y, x;

double sinpi(x)
double x;

double cospi(x)
double x;

void sincospi(x, s, c)
double x, ∗s, ∗c;

double tanpi(x)
double x;

double asinpi(x)
double x;

double acospi(x)
double x;

double atanpi(x)
double x;

double atan2pi(y, x)
double y, x;

DESCRIPTION

sin(), cos(), sincos(), and tan() return trigonometric functions of radian arguments.  The values of trigonometric functions of arguments exceeding π/4 in magnitude are affected by the precision of the approximation to π/2 used to reduce those arguments to the range −π/4 to π/4.  Argument reduction may occur in hardware or software; if in software, the variable fp_pi defined in <math.h> allows changing that precision at run time.  Trigonometric argument reduction is discussed in the Floating-Point Programmer’s Guide.  Note: sincos(x,s,c) allows simultaneous computation of ∗s = sin(x) and ∗c = cos(x). 

asin() returns the arc sin in the range −π/2 to π/2. 

acos() returns the arc cosine in the range 0 to π. 

atan() returns the arc tangent of x in the range −π/2 to π/2. 

atan2(y,x) and hypot(x,y) (see hypot(3M)) convert rectangular coordinates (x,y) to polar (r,θ); atan2() computes θ, the argument or phase, by computing an arc tangent of y/x in the range −π to π.  atan2(0.0,0.0) is ±0.0 or ±π, in conformance with 4.3BSD. 

sinpi(), cospi(), and tanpi() avoid range-reduction issues because their definition sinpi(x)==sin(π∗x) permits range reduction that is fast and exact for all x. The corresponding inverse functions compute asinpi(x)==asin(x)/π.  Similarly atan2pi(y,x)==atan2(y,x)/π. 

DIAGNOSTICS

These functions handle exceptional arguments in the spirit of ANSI/IEEE Std 754-1985.  sin(±∞), cos(±∞), tan(±∞), or asin(x) or acos(x) with |x|>1, return NaN; sinpi(x) et. al. are similar.  In addition, asin(), acos(), and atan2() may also set errno and call matherr(3M). 

SEE ALSO

hypot(3M), matherr(3M)

Solbourne Computer, Inc.  —  13 Dec 1990