CHI
This function evaluates the hyperbolic cosine integral.
Function Return Value
CHI — Function value. (Output)
Required Arguments
X — Argument for which the function value is desired. (Input)
FORTRAN 90 Interface
Generic: CHI (X)
Specific: The specific interface names are S_CHI and D_CHI.
FORTRAN 77 Interface
Single: CHI (X)
Double: The double precision function name is DCHI.
Description
The hyperbolic cosine integral, Chi(x), is defined to be
where
≈ 0.57721566 is Euler’s constant.
The argument x must be large enough that e−x/x does not underflow, and x must be small enough that ex does not overflow.
Comments
When X is negative, the principal value is used.
Example
In this example, Chi(2.5) is computed and printed.
USE CHI_INT
USE UMACH_INT
IMPLICIT NONE
! Declare variables
INTEGER NOUT
REAL VALUE, X
! Compute
X = 2.5
VALUE = CHI(X)
! Print the results
CALL UMACH (2, NOUT)
WRITE (NOUT,99999) X, VALUE
99999 FORMAT (' CHI(', F6.3, ') = ', F6.3)
END
Output
CHI(2.500) = 3.524
