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ATAN2(3) BSD Library Functions Manual ATAN2(3) NAME atan2 -- arc tangent function of two variables SYNOPSIS #include <math.h> double atan2(double y, double x); long double atan2l(long double y, long double x); float atan2f(float y, float x); DESCRIPTION The atan2() function computes the principal value of the arc tangent of y/x, using the signs of both arguments to determine the quadrant of the return value. SPECIAL VALUES atan2(+-0, -0) returns +-pi. atan2(+-0, +0) returns +-0. atan2(+-0, x) returns +-pi for x < 0. atan2(+-0, x) returns +-0 for x > 0. atan2(y, +-0) returns +pi/2 for y > 0. atan2(y, +-0) returns -pi/2 for y < 0. atan2(+-y, -infinity) returns +-pi for finite y > 0. atan2(+-y, +infinity) returns +-0 for finite y > 0. atan2(+-infinity, x) returns +-pi/2 for finite x. atan2(+-infinity, -infinity) returns +-3*pi/4. atan2(+-infinity, +infinity) returns +-pi/4. NOTES The atan2() function is used mostly to convert from rectangular (x,y) to polar (r,theta) coordinates that must satisfy x = r*cos theta and y = r*sin theta. In general, conversions to polar coordinates should be com-puted computed puted thus: r := hypot(x,y); ... := sqrt(x*x+y*y) theta := atan2(y,x). SEE ALSO acos(3), asin(3), atan(3), cos(3), cosh(3), sin(3), sinh(3), tan(3), tanh(3), math(3), STANDARDS The atan2() function conforms to ISO/IEC 9899:1999(E). BSD November 18, 2002 BSD |