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.Dd November 4, 2018
.Dt CSQRT 3
.Os
.Sh NAME
.Nm csqrt ,
.Nm csqrtf ,
.Nm csqrtl
.Nd complex square root functions
.Sh LIBRARY
.Lb libm
.Sh SYNOPSIS
.In complex.h
.Ft double complex
.Fn csqrt "double complex z"
.Ft float complex
.Fn csqrtf "float complex z"
.Ft long double complex
.Fn csqrtl "long double complex z"
.Sh DESCRIPTION
The
.Fn csqrt ,
.Fn csqrtf ,
and
.Fn csqrtl
functions compute the square root of
.Fa z
in the complex plane, with a branch cut along the negative real axis.
In other words,
.Fn csqrt ,
.Fn csqrtf ,
and
.Fn csqrtl
always return the square root whose real part is non-negative.
.Sh RETURN VALUES
These functions return the requested square root.
The square root of 0 is
.Li +0 \*(Pm 0 ,
where the imaginary parts of the input and respective result have
the same sign.
For infinities and \*(Nas, the following rules apply, with the
earlier rules having precedence:
.Bl -column -offset indent "-\*(If + \*(Na*I" "\*(If \*(Pm \*(If*I  " "(for all k)"
.Em "Input" Ta Em "Result" Ta \&
k + \*(If*I	\*(If + \*(If*I	(for all k)
-\*(If + \*(Na*I	\*(Na \*(Pm \*(If*I	\&
\*(If + \*(Na*I	\*(If + \*(Na*I	\&
k + \*(Na*I	\*(Na + \*(Na*I	\&
\*(Na + k*I	\*(Na + \*(Na*I	\&
-\*(If + k*I	+0 + \*(If*I	\&
\*(If + k*I	\*(If + 0*I	\&
.El
.Pp
For numbers with negative imaginary parts, the above special cases
apply given the identity:
.Dl csqrt(conj(z)) = conj(csqrt(z))
Note that the sign of \*(Na is indeterminate.
Also, if the real or imaginary part of the input is finite and
an \*(Na is generated, an invalid exception will be thrown.
.Sh SEE ALSO
.Xr cabs 3 ,
.Xr fenv 3 ,
.Xr math 3
.Sh STANDARDS
The
.Fn csqrt ,
.Fn csqrtf ,
and
.Fn csqrtl
functions conform to
.St -isoC-99 .
.Sh BUGS
For
.Fn csqrt
and
.Fn csqrtl ,
inexact results are not always correctly rounded.