CI

This function evaluates the cosine integral.

Function Return Value

CI — Function value. (Output)

Required Arguments

X — Argument for which the function value is desired. (Input)
It must be greater than zero.

FORTRAN 90 Interface

Generic: CI (X)

Specific: The specific interface names are S_CI and D_CI.

FORTRAN 77 Interface

Single: CI (X)

Double: The double precision function name is DCI.

Description

The cosine integral, Ci(x), is defined to be

 

Where  ≈ 0.57721566 is Euler’s constant.

The argument x must be larger than zero. If

 

then the result will be less accurate than half precision. If x > 1/ɛ, the result will have no precision. Here, ɛ = AMACH(4) is the machine precision.

Example

In this example, Ci(1.5) is computed and printed.

 

USE CI_INT

USE UMACH_INT

 

IMPLICIT NONE

! Declare variables

INTEGER NOUT

REAL VALUE, X

! Compute

X = 1.5

VALUE = CI(X)

! Print the results

CALL UMACH (2, NOUT)

WRITE (NOUT,99999) X, VALUE

99999 FORMAT (' CI(', F6.3, ') = ', F6.3)

END

Output

 

CI( 1.500) = 0.470