Procedure

     APPROX ( Approximate equality )

     LOGICAL FUNCTION APPROX ( X, Y, TOL )

Abstract

     Return .TRUE. if two double precision numbers are equal to 
     within some tolerance.

Required_Reading

     None.

Keywords

     COMPARE
     NUMBERS

Declarations

     IMPLICIT NONE

     DOUBLE PRECISION      X
     DOUBLE PRECISION      Y
     DOUBLE PRECISION      TOL

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     X,
     Y          I   Double precision numbers.
     TOL        I   Tolerance.

     The function is .TRUE. whenever |X - Y| <= TOL.

Detailed_Input

     X,
     Y        are arbitrary double precision numbers.

     TOL      is a tolerance. X and Y are considered to be equal
              if they differ by no more than this amount. If TOL
              is negative, X and Y are never considered equal.

Detailed_Output

     The function is .TRUE. whenever |X - Y| <= TOL, and is .FALSE.
     otherwise.

Parameters

     None.

Exceptions

     Error free.

Files

     None.

Particulars

     None.

Examples

     C
     C     If the eccentricity is near one, this a parabola.
     C
           IF ( APPROX ( ECC, 1.D0, 10.D-12 ) ) THEN
              TYPE = 'PARABOLA'

           ELSE IF ( ECC .LT. 1 ) THEN
              TYPE = 'ELLIPSE'

           ELSE
              TYPE = 'HYPERBOLA'
           END IF

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

     J. Diaz del Rio    (ODC Space)
     W.L. Taber         (JPL)
     I.M. Underwood     (JPL)

Version

    SPICELIB Version 1.1.0, 26-OCT-2021 (JDR)

        Added IMPLICIT NONE statement.

        Edited the header to comply with NAIF standard.

    SPICELIB Version 1.0.1, 10-MAR-1992 (WLT)

        Comment section for permuted index source lines was added
        following the header.

    SPICELIB Version 1.0.0, 31-JAN-1990 (IMU)