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所以,讓我們說我有,我想從(二元正態分佈的混合物)來樣以下2維目標分配 -單組分大都市,黑斯廷斯
import numba
import numpy as np
import scipy.stats as stats
import seaborn as sns
import pandas as pd
import matplotlib.mlab as mlab
import matplotlib.pyplot as plt
%matplotlib inline
def targ_dist(x):
target = (stats.multivariate_normal.pdf(x,[0,0],[[1,0],[0,1]])+stats.multivariate_normal.pdf(x,[-6,-6],[[1,0.9],[0.9,1]])+stats.multivariate_normal.pdf(x,[4,4],[[1,-0.9],[-0.9,1]]))/3
return target
和下面的建議分佈(二元隨機遊走) -
def T(x,y,sigma):
return stats.multivariate_normal.pdf(y,x,[[sigma**2,0],[0,sigma**2]])
下面是在每次迭代更新「整個」狀態的都市黑斯廷斯碼 -
#Initialising
n_iter = 30000
# tuning parameter i.e. variance of proposal distribution
sigma = 2
# initial state
X = stats.uniform.rvs(loc=-5, scale=10, size=2, random_state=None)
# count number of acceptances
accept = 0
# store the samples
MHsamples = np.zeros((n_iter,2))
# MH sampler
for t in range(n_iter):
# proposals
Y = X+stats.norm.rvs(0,sigma,2)
# accept or reject
u = stats.uniform.rvs(loc=0, scale=1, size=1)
# acceptance probability
r = (targ_dist(Y)*T(Y,X,sigma))/(targ_dist(X)*T(X,Y,sigma))
if u < r:
X = Y
accept += 1
MHsamples[t] = X
但是,我想更新「每個組件」(即每個組件)。組件式更新)。有沒有一個簡單的方法來做到這一點?
謝謝您的幫助!
您首先必須計算目標PDF的邊際PDF。然後,您可以按組件明智地採樣'Y [i] = X [i] + stats.norm.rvs(0,sigma,1)'並且也接受/拒絕組件式(即'r =(marg_targ_dist(Y [i ])* T(Y [i],X [i],sigma))/(marg_targ_dist(X [i])* T(X [i],Y [i],sigma))'') – misterkugelblitz