function y = acosh(z)
%ACOSH	Inverse hyperbolic cosine.
%	ACOSH(X) is the inverse hyperbolic cosine of the elements of X.

%	Copyright (c) 1984-93 by The MathWorks, Inc.

% Compute y = log(z + sqrt(z.^2 - 1)) without destructive overflow.
s = max(1,max(abs(real(z)),abs(imag(z))));
y = log(z + s.*sqrt((z./s).^2 - (1./s).^2));
