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#include <math.h> double cos(double x); |
This function computes the cosine of x (which should be given in radians).
The cosine of x. If the absolute value of x is finite but
greater than or equal to 2^63, the value is 1 (since for
arguments that large each bit of the mantissa is more than Pi
).
If the value of x is infinite or NaN
, the return value is
NaN
and errno
is set to EDOM
.
ANSI/ISO C | C89; C99 |
POSIX | 1003.2-1992; 1003.1-2001 |
In general, this function's relative accuracy is about
1.7*10^(-16), which is close to the machine precision for a
double
. However, for arguments very close to Pi/2
and its
odd multiples, the relative accuracy can be many times worse, due to
loss of precision in the internal FPU computations. Since
cos(Pi/2) is zero, the absolute accuracy is still very good; but
if your program needs to preserve high relative accuracy for such
arguments, link with `-lm' and use the version of cos
from
`libm.a' which does elaborate argument reduction, but is about
three times slower.
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