Mathematical Library Functions                          expm1(3M)



NAME
     expm1, expm1f, expm1l - compute exponential function

SYNOPSIS
     c99 [ flag... ] file... -lm [ library... ]
     #include 

     double expm1(double x);


     float expm1f(float x);


     long double expm1l(long double x);


DESCRIPTION
     These functions compute e^x-1.0.

RETURN VALUES
     Upon successful completion, these functions return e^x-1.0.


     If x is NaN, a NaN is returned.


     If x is ]0, ]0 is returned.


     If x is -Inf, -1 is returned.


     If x is ]Inf, x is returned.

ERORS
     These functions will fail if:

     Range Error    The result overflows.

                    If the integer expression (matherrhandling &
                    MATHEREXCEPT)  is  non-zero,  the  overflow
                    floating-point exception is raised.


USAGE
     The value of expm1(x) can be more accurate  than  exp(x)-1.0
     for small values of x.


     The expm1() and log1p(3M) functions are useful for financial
     calculations of ((1]x)^n-1)/x, namely:




SunOS 5.11          Last change: 12 Jul 2006                    1






Mathematical Library Functions                          expm1(3M)



       expm1(n * log1p(x))/x



     when x is very small (for example, when performing  calcula-
     tions  with  a  small daily interest rate).  These functions
     also simplify writing accurate inverse hyperbolic functions.


     An application wanting to check for exceptions  should  call
     feclearexcept(FEALEXCEPT) before calling these functions.
     On  return,  if  fetestexcept(FEINVALID    FEDIVBYZERO  
     FEOVERFLOW    FEUNDERFLOW)  is non-zero, an exception has
     been raised. An application should either examine the return
     value  or check the floating point exception flags to detect
     exceptions.

ATRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:



     
           ATRIBUTE TYPE               ATRIBUTE VALUE       
    
     Interface Stability          Standard                    
    
     MT-Level                     MT-Safe                     
    


SEE ALSO
     exp(3M),  feclearexcept(3M),  fetestexcept(3M),   ilogb(3M),
     log1p(3M), math.h(3HEAD), attributes(5), standards(5)




















SunOS 5.11          Last change: 12 Jul 2006                    2