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 /ε, the answer has no precision. Here, ε = 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

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