Mathematica の式(d)

f8[x_, y_, mu1_, mu2_, sigm1_, sigm2_, rho_, y0_] := 
  Exp[((x - mu1)^2/sigm1^2 + (y - mu2)^2/sigm2^2 - 
                        2 rho(x - mu1)(y - mu2)/sigm1/sigm2)/(-2)/(1 - 
                      rho^2)]/2/Pi/sigm1/sigm2/Sqrt[1 - rho^2] /; y >= y0
f8[x_, y_, mu1_, mu2_, sigm1_, sigm2_, rho_, y0_] := 0 /; y < y0
Plot3D[f8[x, y, 0, 0, 1, 1, 0.7, 1], {x, -3, 3}, {y, -3, 3}, 
  PlotPoints -> 50, PlotRange -> All, Axes -> {False, False, False}, 
  Boxed -> False, ViewPoint -> {0.0, -2.4, 2.}]