SI

This function evaluates the sine integral.

Function Return Value

SI — Function value. (Output)

Required Arguments

X — Argument for which the function value is desired. (Input)

FORTRAN 90 Interface

Generic: SI (X)

Specific: The specific interface names are S_SI and D_SI.

FORTRAN 77 Interface

Single: SI (X)

Double: The double precision function name is DSI.

Description

The sine integral, Si(x), is defined to be

 

If

 

the answer is less accurate than half precision, while for ∣x∣ > 1 /ɛ, the answer has no precision. Here, ɛ = AMACH(4) is the machine precision.

Example

In this example, Si(1.25) is computed and printed.

 

USE SI_INT

USE UMACH_INT

 

IMPLICIT NONE

! Declare variables

INTEGER NOUT

REAL VALUE, X

! Compute

X = 1.25

VALUE = SI(X)

! Print the results

CALL UMACH (2, NOUT)

WRITE (NOUT,99999) X, VALUE

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

END

Output

 

SI( 1.250) = 1.146