[求助]如何模拟三维正态图？

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老板布置任务，刚开始学习R，不太熟习，请教大家

先谢谢啦！！！！

现在，我用命令

library(MASS)

sigma<-matrix(c(1,0.5,0.5,1),2,2);

X<-mvrnorm(100,c(0,0),sigma);

产生了100个二维正态随机数，怎么产生它的三维图表示？

请大侠指点！！

[em12][em12]

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关键词：Library Sigma BRARY mass mas 求助 模拟 三维

You need to calculate the density for each element of an array whose rows correspond to x values, and columns to y values. And then use persp to draw the 3d plot. Hope the following helps.

library(MASS)
sigma<-matrix(c(1,0.5,0.5,1),2,2);
X<-mvrnorm(100,c(0,0),sigma);


x<-seq(-3,3,by=.01)
y<-x
phi<-function(x,y)
{sigma=cor(X)[1,2]
exp(-(x^2-2*sigma*x*y+y^2)/2/(1-sigma^2))/2/pi/sqrt(1-sigma^2)
}
z <- outer(x, y, phi)
persp(x,y,z,theta=30,phi=30,col="lightblue",shade=.3,border=NA)
title(paste("bivariate normal distribution with cor=",round(cor(X)[1,2],3)))

 

Thank you! This sentence ‘exp(-(x^2-2*sigma*x*y+y^2)/2/(1-sigma^2))/2/pi/sqrt(1-sigma^2)’ is puzzling for me! If we don't know these data is obtained from the normal distrbution, we only have these data,how can I do? I found a package 'rgl' which is used for 3D , #**********************alpha正态污染图***************************** alpha=0.1;sigma=5; fn=function(x,y){(1-alpha)/(2*pi)*exp(-(x^2+y^2)/2)+ alpha/(2*pi*sigma)*exp(-(x^2+y^2)/(2*sigma))  } x<-seq(-2,2,len=17);y<-seq(-2,2,len=17); z<-outer(x,y,fn); color<-rainbow(41)[1+round(10*outer(x,y,fn))]  ; library(rgl)         #rgl为专门画3D图的包 persp3d(x,y,z,color=color,smooth=FALSE) surface3d(x,y,z+0.01,front="lines",back="culled") #******************使图像自动旋转********************************** M <- par3d("userMatrix") play3d( par3dinterp( userMatrix=list(M,                                      rotate3d(M, pi/2, 1, 0, 0),                                      rotate3d(M, pi/2, 0, 1, 0) ) ),         duration=4 ) movie3d( spin3d(), duration=5 ) #****************************************************************** Please check for me ,if you can draw a little time! Thank you very much!

[此贴子已经被作者于2009-3-14 11:59:36编辑过]

that expression "exp(-(x^2-2*sigma*x*y+y^2)/2/(1-sigma^2))/2/pi/sqrt(1-sigma^2)" is the expression for bivariate-normal distribution density function.

if you have no prior knowledge about the distribution of your data. there is not too much you can do. maybe use some non-parametric methods to estimate their potential distributions.

If you want to plot 3D. you can also use the function contour(),the details you can get form the help files.

顶

 

thank you very much!

he,I have found a package scatterplot3d

which can be used to plot 3 dim scatterplot.

 

 

[em01][em01][em01]

2# vrooadk

那如果有两个二维正态分布呢？要想把它们的分布图在一张图里画出来，可以么？谢谢~~~

How to get rgl? I can not find it

顶下，我正找3D的包