Procedure

     SMSGND  ( Same Sign Double Precision Numbers )

     LOGICAL FUNCTION SMSGND ( X, Y )

Abstract

     Return .TRUE. if two given double precision numbers have the same
     sign.

Required_Reading

     None.

Keywords

     NUMBERS

Declarations

     IMPLICIT NONE

     DOUBLE PRECISION   X
     DOUBLE PRECISION   Y

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     X          I   A double precision number
     Y          I   A double precision number

     The function returns .TRUE. if the input arguments have the same
     sign.

Detailed_Input

     X        is any double precision number.

     Y        is any double precision number.

Detailed_Output

     The function returns .TRUE. if X and Y are both positive or both
     negative. Otherwise, it returns .FALSE.

Parameters

     None.

Exceptions

     Error free.

Files

     None.

Particulars

     This routine returns the value:

           (      (( X .GT. 0) .AND. (Y .GT. 0))
             .OR. (( X .LT. 0) .AND. (Y .LT. 0)) )

     This is a more stable value than

           ( X*Y .GT. 0 )

     Note: If either of the to inputs is zero. The result returned
     will be .FALSE.

Examples

     This routine can be used whenever a decision depends upon two
     Double Precision values having the same sign.

     IF ( SMSGND ( F(X1), F(X2) ) ) THEN
           .
           .
        do something
           .
           .
     ELSE
           .
           .
        find a root of F lying between X1 and X2
           .
           .
     END IF

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

     J. Diaz del Rio    (ODC Space)
     W.L. Taber         (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 (WLT)