SWI-Prolog -- function sign/1

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Function sign/1

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Documentation
- Reference manual
  - Built-in Predicates
    - Arithmetic
      - General purpose arithmetic
        
        Arithmetic Functions
        
        -/1
        
        +/1
        
        +/2
        
        -/2
        
        */2
        
        //2
        
        mod/2
        
        rem/2
        
        ///2
        
        div/2
        
        rdiv/2
        
        gcd/2
        
        lcm/2
        
        abs/1
        
        sign/1
        
        cmpr/2
        
        copysign/2
        
        nexttoward/2
        
        roundtoward/2
        
        max/2
        
        maxr/2
        
        min/2
        
        minr/2
        
        ./2
        
        random/1
        
        random_float/0
        
        round/1
        
        integer/1
        
        float/1
        
        rational/1
        
        rationalize/1
        
        numerator/1
        
        denominator/1
        
        float_fractional_part/1
        
        float_integer_part/1
        
        truncate/1
        
        floor/1
        
        ceiling/1
        
        ceil/1
        
        >>/2
        
        <</2
        
        \//2
        
        /\/2
        
        xor/2
        
        \/1
        
        sqrt/1
        
        sin/1
        
        cos/1
        
        tan/1
        
        asin/1
        
        acos/1
        
        atan/1
        
        atan2/2
        
        atan/2
        
        sinh/1
        
        cosh/1
        
        tanh/1
        
        asinh/1
        
        acosh/1
        
        atanh/1
        
        log/1
        
        log10/1
        
        exp/1
        
        **/2
        
        ^/2
        
        powm/3
        
        lgamma/1
        
        erf/1
        
        erfc/1
        
        pi/0
        
        e/0
        
        epsilon/0
        
        inf/0
        
        nan/0
        
        cputime/0
        
        eval/1
        
        msb/1
        
        lsb/1
        
        popcount/1
        
        getbit/2
- Packages

Availability:Arithmetic function (see is/2)

[ISO]sign(+Expr)

Evaluate to -1 if Expr < 0, 1 if Expr > 0 and 0 if Expr = 0. If Expr evaluates to a float, the return value is a float (e.g., -1.0, 0.0 or 1.0). In particular, note that sign(-0.0) evaluates to 0.0. See also copysign/2.