acos function

Synopsis

$acos(number)

Technical

acos() calls the C library's acos() function to return the principal arc cosine of number. For a number between -1 and 1 inclusive, the result is an angle between zero and pi radians. It does not return degrees. cos() performs the corresponding cosine operation.

The normal rules about number arguments apply. The first argument word is converted with atof(), accepting decimal fractions and scientific notation; further words are ignored. Missing input returns the empty string. Nonnumeric input converts to zero, and trailing nonnumeric characters do not necessarily prevent a numeric prefix from being used.

Returns and restrictions

Results use a C double and are formatted with %.50g. The floating_point_math and floating_point_precision settings do not change this function's calculation or formatting. The long result string can expose rounding digits; it does not imply 50 digits of accuracy.

Arguments outside [-1, 1] cause a domain error in the library operation. EPIC returns DOM if the library reports that error through errno; a platform that reports it only as a floating-point exception can instead produce a NaN result string. The wrapper also returns RANGE for a reported range error, or the empty string for another reported error. It checks errno, not floating-point exception flags. Validate the argument's range rather than relying on one particular error string.

Examples

The approximate examples describe the numeric value; the returned string may contain more digits.

Source

source/functions.c registers acos and implements function_acos through the shared math-function and error-return macros. include/functions.h defines argument conversion and formatting. The C/POSIX arc cosine specification defines radians, the valid range, and library error reporting.