problem evaluating negative numbers

The plot of the following function is correct, but when negative values are evaluated, they do not correspond to the plot

documentclass[border=1pt]{standalone}

usepackage[dvipsnames,svgnames,x11names,]{xcolor}
usepackage{pgf,tikz,tikz-3dplot}
usepackage{pgfplots}

pgfplotsset{compat=1.12}


begin{document}
    

pgfmathsetmacro{xi}{-2.5} %value
    begin{tikzpicture}[line cap=round,line join=round, font={small }]
        begin{axis}[height=6cm,width=10cm,no markers,  axis lines=center, xlabel={$x$}, 
            ylabel={$F(x)$},
            xmin=-9,xmax=9,
            ymin=-7,ymax=7,
            declare function={
                erf(x)=%
                (1+(e^(-(x*x))*(-265.057+abs(x)*(-135.065+abs(x)%
                *(-59.646+(-6.84727-0.777889*abs(x))*abs(x)))))%
                /(3.05259+abs(x))^5)*(x>0?1:-1);
                f(x)=(-0.5*x^3+3.8*x^2+4*x+1)*exp(-0.6*x^2);
                Fa(x)=0.5*exp(-0.6*x^2)*(-(-0.5)*0.6*x^2-3.8*0.6*x-4*0.6+0.5)/(0.6^2);
                Fb(x)=-0.25*sqrt(pi)*(2*0.6+3.8)*erf(-sqrt(0.6)*x)/(0.6*sqrt(0.6));
                F(x)=Fa(x)+Fb(x);
            }, 
            ]
            addplot[domain=-5:5, samples=41, smooth, SteelBlue1, line width=1pt]{F(x)};
            
            draw[dash pattern=on1pt off 1pt, ] (xi,0)-- (xi,{F(xi)});
            
            draw[gray] (xi,0.2) -- (xi, -0.2);
            
            draw[, DodgerBlue3] (0,{F(xi)})-- (xi,{F(xi)});
            node[font=tiny] at (4,-5) {$F(a)=pgfmathparse{F(xi)}pgfmathresult$};
        end{axis}
    end{tikzpicture}
end{document}

Im using this erf function Erf function in LaTeX

documentclass[border=1pt]{standalone}
usepackage[dvipsnames,svgnames,x11names,]{xcolor}
%usepackage{pgf,tikz,tikz-3dplot}
usepackage{pgfplots}
pgfplotsset{compat=1.12} % recent is 1.17, I suggest you to upgrade it

begin{document}
pgfmathsetmacro{xi}{-2.5} %value
    begin{tikzpicture}[line cap=round,line join=round, font={small }]
        begin{axis}[height=6cm,width=10cm,no markers,  axis lines=center, xlabel={$x$},
            ylabel={$F(x)$},
            xmin=-9,xmax=9,
            ymin=-7,ymax=7,
            declare function={
                erf(x)=%
                (1+(e^(-(x*x))*(-265.057+abs(x)*(-135.065+abs(x)%
                *(-59.646+(-6.84727-0.777889*abs(x))*abs(x)))))%
                /(3.05259+abs(x))^5)*(x>0?1:-1);
                f(x)=(-0.5*x^3+3.8*x^2+4*x+1)*exp(-0.6*x^2);
                Fa(x)=0.5*exp(-0.6*(x)^2)*(-(-0.5)*0.6*(x)^2-3.8*0.6*x-4*0.6+0.5)/(0.6^2);
                Fb(x)=-0.25*sqrt(pi)*(2*0.6+3.8)*erf(-sqrt(0.6)*x)/(0.6*sqrt(0.6));
                F(x)=Fa(x)+Fb(x);
            },
            ]
            addplot[domain=-5:5, samples=41, smooth, SteelBlue1, line width=1pt]{F(x)};

            draw[dash pattern=on1pt off 1pt, ] (xi,0)-- (xi,{F(xi)});

            draw[gray] (xi,0.2) -- (xi, -0.2);

            draw[, DodgerBlue3] (0,{F(xi)})-- (xi,{F(xi)});
            node[font=tiny] at (4,-5) {$F(a)=pgfmathparse{F(xi)}pgfmathresult$};
        end{axis}
    end{tikzpicture}
end{document}