#define acosh( z )
(4) (since C99)1-3) Computes complex arc hyperbolic cosine of a complex value z
with branch cut at values less than 1 along the real axis.
Type-generic macro: If
z
has type
long double complex,
cacoshl
is called. if
z
has type
double complex,
cacosh
is called, if
z
has type
float complex,
cacoshf
is called. If
z
is real or integer, then the macro invokes the corresponding real function (
acoshf,
acosh,
acoshl). If
z
is imaginary, then the macro invokes the corresponding complex number version and the return type is complex.
[edit] Parameters [edit] Return valueThe complex arc hyperbolic cosine of z
in the interval [0; â) along the real axis and in the interval [âiÏ; +iÏ] along the imaginary axis.
Errors are reported consistent with math_errhandling
If the implementation supports IEEE floating-point arithmetic,
z
is ±0+0i
, the result is +0+iÏ/2
z
is +x+âi
(for any finite x), the result is +â+iÏ/2
z
is +x+NaNi
(for non-zero finite x), the result is NaN+NaNi
and FE_INVALID may be raised.z
is 0+NaNi
, the result is NaN±iÏ/2
, where the sign of the imaginary part is unspecifiedz
is -â+yi
(for any positive finite y), the result is +â+iÏ
z
is +â+yi
(for any positive finite y), the result is +â+0i
z
is -â+âi
, the result is +â+3iÏ/4
z
is +â+âi
, the result is +â+iÏ/4
z
is 屉+NaNi
, the result is +â+NaNi
z
is NaN+yi
(for any finite y), the result is NaN+NaNi
and FE_INVALID may be raised.z
is NaN+âi
, the result is +â+NaNi
z
is NaN+NaNi
, the result is NaN+NaNi
Although the C standard names this function "complex arc hyperbolic cosine", the inverse functions of the hyperbolic functions are the area functions. Their argument is the area of a hyperbolic sector, not an arc. The correct name is "complex inverse hyperbolic cosine", and, less common, "complex area hyperbolic cosine".
Inverse hyperbolic cosine is a multivalued function and requires a branch cut on the complex plane. The branch cut is conventionally placed at the line segment (-â,+1) of the real axis.
The mathematical definition of the principal value of the inverse hyperbolic cosine is acosh z = ln(z + âz+1 âz-1)
For any z,
acosh(z) = acos(z), or simply
i acos(z)in the upper half of the complex plane.
[edit] Example#include <stdio.h> #include <complex.h> int main(void) { double complex z = cacosh(0.5); printf("cacosh(+0.5+0i) = %f%+fi\n", creal(z), cimag(z)); double complex z2 = conj(0.5); // or cacosh(CMPLX(0.5, -0.0)) in C11 printf("cacosh(+0.5-0i) (the other side of the cut) = %f%+fi\n", creal(z2), cimag(z2)); // in upper half-plane, acosh(z) = i*acos(z) double complex z3 = casinh(1+I); printf("casinh(1+1i) = %f%+fi\n", creal(z3), cimag(z3)); double complex z4 = I*casin(1+I); printf("I*asin(1+1i) = %f%+fi\n", creal(z4), cimag(z4)); }
Output:
cacosh(+0.5+0i) = 0.000000-1.047198i cacosh(+0.5-0i) (the other side of the cut) = 0.500000-0.000000i casinh(1+1i) = 1.061275+0.666239i I*asin(1+1i) = -1.061275+0.666239i[edit] References
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