[使用MATLAB中大型矩阵的特征向量获得马尔可夫链的平稳分布

问题描述 投票:0回答:1

我试图找到马尔可夫链的平稳分布。我有一个转移概率矩阵(TPM)。这是代码:

[V, D] = eigs(double(TPM'),1); 
Py = abs(V)/sum(V);

我的问题是sum(V) < 0,所以它在矢量Py中给了我一些负值。我已经使用另一个概率矩阵测试了代码,结果为sum(V) > 0

我不知道这是什么问题,是TPM还是我使用的代码?

编辑:

这里是代码的更“精巧”版本(包括“ SecretAgentMan”的答案,请参见方法3):

function [Py1, Py2, Py3] = testStatDist(TPM)

% method 1
[V1, D1] = eigs(double(TPM'),1);

% method 2
[V2, D2] = iterator(TPM);

% method 3
V3 = null(eye(size(TPM))-TPM.'); 

if(abs(D1 - 1) > 1e-5)
    warning(0, 'testStatDist.m: Check Transition Matrix');
    exit;
end

if(abs(D2 - 1) > 1e-5)
    warning(0, 'testStatDist.m: Check Transition Matrix');
    exit;
end

% res 1
Py1 = abs(V1)/sum(V1);

% res 2
Py2 = abs(V2)/sum(V2);

% res 3
Py3 = abs(V3)/sum(V3);
end

这里是函数“迭代器”:

function [V, D] = iterator(TPM)

pi(1:length(TPM)) = 1/length(TPM);
error = 1;
budget = 1000;
while(error >= 1e-10)
    pi2 = pi*TPM;
    error = sum((pi - pi2).^2);
    pi = pi2;
    budget = budget - 1;
    if(budget == 0)
        break;
    end
end
V = pi';
D = 1;

这是我正在使用的TPM之一:

TPM = [0.987665198237886    0.000220264317180617    0.000440528634361233    0.000660792951541850    0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0.000881057268722467    0.985682819383260   0.00110132158590308 0.00132158590308370 0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0.00154185022026432 0.00176211453744493 0.983700440528634   0.00198237885462555 0   0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0.988986784140969   0   0   0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0.00440528634361233 0   0   0   0.983259911894273   0.000220264317180617    0.000440528634361233    0.000660792951541850    0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0.00440528634361233 0   0   0.000881057268722467    0.981277533039648   0.00110132158590308 0.00132158590308370 0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0.00440528634361233 0   0.00154185022026432 0.00176211453744493 0.979295154185022   0.00198237885462555 0   0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0.00440528634361233 0   0   0   0.984581497797357   0   0   0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0   0.00881057268722467 0   0   0   0.978854625550661   0.000220264317180617    0.000440528634361233    0.000660792951541850    0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0   0   0.00881057268722467 0   0   0.000881057268722467    0.976872246696035   0.00110132158590308 0.00132158590308370 0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0   0   0   0.00881057268722467 0   0.00154185022026432 0.00176211453744493 0.974889867841410   0.00198237885462555 0   0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
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0   0   0   0   0   0   0   0   0   0.0132158590308370  0   0   0.000881057268722467    0.972466960352423   0.00110132158590308 0.00132158590308370 0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0   0   0   0.0132158590308370  0   0.00154185022026432 0.00176211453744493 0.970484581497797   0.00198237885462555 0   0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0   0   0   0   0.0132158590308370  0   0   0   0.975770925110132   0   0   0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0   0   0   0   0   0.0176211453744493  0   0   0   0.970044052863436   0.000220264317180617    0.000440528634361233    0.000660792951541850    0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0   0   0   0   0   0   0.0176211453744493  0   0   0.000881057268722467    0.968061674008811   0.00110132158590308 0.00132158590308370 0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0   0   0   0   0   0   0   0.0176211453744493  0   0.00154185022026432 0.00176211453744493 0.966079295154185   0.00198237885462555 0   0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0.0176211453744493  0   0   0   0.971365638766520   0   0   0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0.0220264317180617  0   0   0   0.965638766519824   0.000220264317180617    0.000440528634361233    0.000660792951541850    0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0.0220264317180617  0   0   0.000881057268722467    0.963656387665198   0.00110132158590308 0.00132158590308370 0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0.0220264317180617  0   0.00154185022026432 0.00176211453744493 0.961674008810573   0.00198237885462555 0   0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
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0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0.0264317180616740  0   0   0   0.961233480176212   0.000220264317180617    0.000440528634361233    0.000660792951541850    0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0.0264317180616740  0   0   0.000881057268722467    0.959251101321586   0.00110132158590308 0.00132158590308370 0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0.0264317180616740  0   0.00154185022026432 0.00176211453744493 0.957268722466960   0.00198237885462555 0   0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0.0264317180616740  0   0   0   0.962555066079295   0   0   0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0.0308370044052863  0   0   0   0.956828193832599   0.000220264317180617    0.000440528634361233    0.000660792951541850    0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
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0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0.0308370044052863  0   0.00154185022026432 0.00176211453744493 0.952863436123348   0.00198237885462555 0   0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0.0308370044052863  0   0   0   0.958149779735683   0   0   0   0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0.0352422907488987  0   0   0   0.952422907488987   0.000220264317180617    0.000440528634361233    0.000660792951541850    0.0110132158590308  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
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0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0.0792951541850220  0   0   0   0.909691629955947   0   0   0   0.0110132158590308  0   0   0   0
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0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0.0881057268722467  0   0.00154185022026432 0.00176211453744493 0.906607929515419   0.00198237885462555
0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0.0881057268722467  0   0   0   0.911894273127753];

问题1:

这3种方法中的每一种都会产生不同的结果,我不确定该使用哪种方法。对于迭代器方法,我知道在大TPM的情况下可以使用近似值。

为什么值会有这样的差异?

问题2:

为什么我在平稳分布中得到负值?我使用了较大的TPM,大小为2600x2600,但没有得到任何负值,但是很难在此处放置2600x2600矩阵。

matlab eigenvalue eigenvector markov-chains
1个回答
0
投票

不需要工具箱:我们知道稳态概率是离散时间马尔可夫链(DTMC)下方程的唯一解。

Equations to find steady state distribution (probabilities) for a discrete time Markov chain

您可以重写此内容以表明此分布必须位于转换概率矩阵的零空间中(请参见下文)。这允许使用MATLAB的null()

null()

对总和进行归一化给出唯一的解,并且满足另一个方程式。

Rewriting the steady state equations to show the steady state distribution lies in the null space of the transition probability matrix

注意,临时P = [.2 .3 .3 0 .2; .1 .2 .3 .4 0; 0 .5 .4 .1 0; .2 .2 .2 .3 .1; .5 .2 .1 .1 .1]; ssp0 = null(eye(size(P))-P.'); SteadyStateProb = ssp0./sum(ssp0) % [0.1263 0.3017 0.2969 0.2224 0.0528] 具有负值,但最终答案ssp0是正确的,因为所有值均为有效概率,所有概率之和为1。


基于SteadyStateProb的更新:条件矩阵

您的转换概率矩阵的问题之一,即您编辑中的84×84大小OP's edit,是行总和大于一。您可以使用TPM进行验证,以获取发生这种情况的行索引。此外,此“超量”非常小:find(sum(TPM,2) > 1)显示最大行总和超过1乘以max(sum(TPM,2))-1,对于我来说,是4.4409e-16eps)的两倍。

使用下面技术含量很低的代码,我对每一行进行了规范化。

2.2204e-16

这将导致行总数不超过一;您可以使用% Re-Normalize: Divide the kth row by the sum of that row TPM2 = TPM; for k = 1:size(TPM2,1) TPM2(k,:) = TPM2(k,:)/sum(TPM2(k,:)); end 进行验证,该方法将返回一个0×1的空双列向量。

无需进一步按摩矩阵,我们就可以获得稳态下的分布。

find(sum(TPM2,2) > 1)

注意ssp0 = null(eye(size(TPM2))-TPM2.'); SteadyStateProb_TPM2 = ssp0./sum(ssp0); min(SteadyStateProb_TPM2)(零!),且总和基本上为1(-9.6502e-16)。

我现在要强制非负性。

abs(1-sum(SteadyStateProb_TPM2))

比较迭代近似值:我们知道,随着SteadyStateProb_TPM2(SteadyStateProb_TPM2<0) = 0; 变得足够大,TPM2^n会收敛到SteadyStateProb_TPM2。因此,让我们检查一下。

我们将转移矩阵本身乘以很多次(这里我们得到2500步的转移矩阵)。我们可以看到它似乎或多或少地集中在目标上。

n

ans =

Approx = TPM2^500;
Approx = Approx*Approx*Approx*Approx*Approx; 

ind = find(SteadyStateProb_TPM2 > 0.05); % find states with steady state prob > 0.05

SteadyStateProb_TPM2(ind).'
Approx(1:6,ind)

ans =

0.0821    0.2052    0.2565    0.2138    0.1336    0.0668

取决于您的应用程序,您可能会认为此迭代方法足够好,但是当直接分析方法仍然可行时,我将不使用它。我想如果您花点时间确保条件良好,那么在MATLAB中2600×2600矩阵是可行的。

更新版本:0.0727 0.1818 0.2273 0.1894 0.1184 0.0592 0.0760 0.1900 0.2374 0.1979 0.1237 0.0618 0.0763 0.1908 0.2385 0.1988 0.1242 0.0621 0.0821 0.2052 0.2565 0.2138 0.1336 0.0668 0.0727 0.1818 0.2273 0.1894 0.1184 0.0592 0.0760 0.1900 0.2374 0.1979 0.1237 0.0618 :特征值方法呢?

效果很好。

OP's comment

或替代地,

% Using the 5x5 P matrix from above
[V,D] = eigs(double(P.'),1);
Py = -abs(V)/sum(V)

[您也可以在84x84上验证此功能:

Pyalt = V./sum(V)

给出以下内容。

[V2,D2] = eigs(double(TPM2'),1); Py_TPM2 = -abs(V2)/sum(V2); Py_TPM2alt = V2./sum(V2); % Evaluate to compare SteadyStateProb_TPM2(ind).' Py_TPM2(ind).' Py_TPM2alt(ind).' SteadyStateProb_TPM2(ind).' = 0.0821 0.2052 0.2565 0.2138 0.1336 0.0668Py_TPM2(ind).' = 0.0821 0.2052 0.2565 0.2138 0.1336 0.0668

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