Mathematica の式(b) f4[x_, y_, mu1_, mu2_, sigm1_, sigm2_, rho_] := 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] Plot3D[f4[x, y, 0, 0, 1, 1, 0.0], {x, -3, 3}, {y, -3, 3}, PlotPoints -> 30, PlotRange -> All, ViewPoint -> {0.0, -2.4, 2.}]