.\" Stephen Canon, Apple Inc .Dd July 6, 2010 .Dt M_PI 3 .Os .Sh NAME .Nm constants .Nd mathematical library constants .Sh SYNOPSIS .Fd #include <math.h> .Sh DESCRIPTION The header file math.h provides macros that define a number of useful numerical constants. .Sh LIST OF CONSTANTS As required by the POSIX standard, these constants are double-precision literals, with enough digits specified as to ensure that they are correctly rounded in double-precision: .Pp .Dv M_E .Pp "Euler's constant" or e; the base of the natural logarithm. .Pp .Dv M_LOG2E .br .Dv M_LOG10E .Pp The logarithms of e in base 2 and 10, respectively. .Pp .Dv M_LN2 .br .Dv M_LN10 .Pp The natural logarithms of 2 and 10, respectively. Note that these are the reciprocals of the preceeding two values. .Pp .Dv M_PI .br .Dv M_PI_2 .br .Dv M_PI_4 .Pp pi, pi/2, and pi/4, respectively. .Pp .Dv M_1_PI .br .Dv M_2_PI .Pp 1/pi and 2/pi, respectively. .Pp .Dv M_2_SQRTPI .Pp Two divided by the square root of pi. .Pp .Dv M_SQRT2 .br .Dv M_SQRT_1_2 .Pp The square root of two and its reciprocal, respectively. .Sh SEE ALSO .Xr math 3 , .Xr float 3 , .Sh STANDARDS The <math.h> functions and macros conform to the ISO/IEC 9899:1999(E) standard.