import graph3;
size(7.5cm,0);
real f(pair z) {return -exp(-abs(z)^2);}
currentprojection=perspective(4,5,4);
limits(O,2.25(1,1,1));
xaxis3(Label("$x$",1),blue,arrow=Arrow3);
yaxis3(Label("$y$",1),blue,arrow=Arrow3);
zaxis3(Label("$z$",1),blue,arrow=Arrow3);
draw(surface(f,(-2,-2),(2,2),nx=20,Spline),
     lightgray,meshpen=black+thick(),nolight);
dot(Label("$O$",align=Z+X),(0,0,0),red);