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
