man3p/atan.3p

   1 .\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
   2 .TH "ATAN" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
   3 .\" atan
   4 .SH NAME
   5 atan, atanf, atanl \- arc tangent function
   6 .SH SYNOPSIS
   7 .LP
   8 \fB#include <math.h>
   9 .br
  10 .sp
  11 double atan(double\fP \fIx\fP\fB);
  12 .br
  13 float atanf(float\fP \fIx\fP\fB);
  14 .br
  15 long double atanl(long double\fP \fIx\fP\fB);
  16 .br
  17 \fP
  18 .SH DESCRIPTION
  19 .LP
  20 These functions shall compute the principal value of the arc tangent
  21 of their argument \fIx\fP.
  22 .LP
  23 An application wishing to check for error situations should set \fIerrno\fP
  24 to zero and call
  25 \fIfeclearexcept\fP(FE_ALL_EXCEPT) before calling these functions.
  26 On return, if \fIerrno\fP is non-zero or
  27 \fIfetestexcept\fP(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
  28 is non-zero, an error has occurred.
  29 .SH RETURN VALUE
  30 .LP
  31 Upon successful completion, these functions shall return the arc tangent
  32 of \fIx\fP in the range [-pi/2,pi/2] radians.
  33 .LP
  34 If
  35 \fIx\fP is NaN, a NaN shall be returned.
  36 .LP
  37 If \fIx\fP is \(+-0, \fIx\fP shall be returned.
  38 .LP
  39 If \fIx\fP is \(+-Inf, \(+-pi/2 shall be returned.
  40 .LP
  41 If \fIx\fP is subnormal, a range error may occur and \fIx\fP should
  42 be returned.
  43 .SH ERRORS
  44 .LP
  45 These functions may fail if:
  46 .TP 7
  47 Range\ Error
  48 The value of \fIx\fP is subnormal.
  49 .LP
  50 If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
  51 then \fIerrno\fP shall be set to [ERANGE]. If the
  52 integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
  53 then the underflow floating-point exception shall be
  54 raised.
  55 .sp
  56 .LP
  57 \fIThe following sections are informative.\fP
  58 .SH EXAMPLES
  59 .LP
  60 None.
  61 .SH APPLICATION USAGE
  62 .LP
  63 On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling
  64 & MATH_ERREXCEPT) are independent of
  65 each other, but at least one of them must be non-zero.
  66 .SH RATIONALE
  67 .LP
  68 None.
  69 .SH FUTURE DIRECTIONS
  70 .LP
  71 None.
  72 .SH SEE ALSO
  73 .LP
  74 \fIatan2\fP() , \fIfeclearexcept\fP() , \fIfetestexcept\fP() , \fIisnan\fP()
  75 , \fItan\fP() , the
  76 Base Definitions volume of IEEE\ Std\ 1003.1-2001, Section 4.18, Treatment
  77 of Error Conditions for Mathematical Functions, \fI<math.h>\fP
  78 .SH COPYRIGHT
  79 Portions of this text are reprinted and reproduced in electronic form
  80 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
  81 -- Portable Operating System Interface (POSIX), The Open Group Base
  82 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
  83 Electrical and Electronics Engineers, Inc and The Open Group. In the
  84 event of any discrepancy between this version and the original IEEE and
  85 The Open Group Standard, the original IEEE and The Open Group Standard
  86 is the referee document. The original Standard can be obtained online at
  87 http://www.opengroup.org/unix/online.html .