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(PHP 4 >= 4.1.0, PHP 5)

asinhInverse hyperbolic sine


float asinh ( float $arg )

Returns the inverse hyperbolic sine of arg, i.e. the value whose hyperbolic sine is arg.



The argument to process

Return Values

The inverse hyperbolic sine of arg


Version Description
5.3.0 This function is now available on all platforms

See Also

User Contributed Notes
ape_cwb at yahoo dot com dot br
15-Nov-2007 01:40
The correct implementation of asinh(x) for Windows plataform is:

function asinh($x)
        return ln($x + sqrt(1 + pow($x, 2)));

function ln($x)
     return $x = log($x)/log(M_E);

The worksheet above includes a comparation about the native asinh(x) and the implemented version using LN and LOG (like Snoyes posted on 27-Dec-2005 07:42)


This implementation using LN, give THE SAME results that function asinh(x) linux native.

Allan Patrick Engel
Curitiba - ParanĂ¡ - Brasil
08-Jun-2007 07:57
When using snoyes alternative bcasinh function, don't forget to check the precision of each single bcfunction or the default precision of ini setting bcmath.scale.
snoyes at gmail dot com
27-Dec-2005 03:42
asinh for windows:

The definition for asinh is asinh(z) = log(z + sqrt(z^2 + 1))

The built-in math functions and operators give poor results for small values of z.  The BCMath version produces closer results, but still quite distant if z < 1.  A BCMath version of the log function might help.

if (!function_exists("asinh")) {
    function asinh($z) {
      return log($z + sqrt($z^2 +1));

if (!function_exists("bcasinh")) {
    function bcasinh($z) {
      return log(bcadd($z, bcsqrt(bcadd(bcpow($z, 2), 1))));

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