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 γ ≈ 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/ε, the result will have no precision.  Here, ε = 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

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