[statnet_help] issues with dyadcov # Error in solve.default(H, tol = 1e-20) : Lapack routine dgesv: system is exactly singular: U[11, 11] = 0

汪翩翩 pian.wang at szu.edu.cn
Mon Apr 20 05:47:28 PDT 2020


Hello statnet community,



I have a question regarding to “dyadcov”. I’m trying to use the term “dyadcov” to test the influence of a follower-followee network of a group of people on the formation of their communication network. But several error messages popping up during this process.

The follower-followee network (ff) and communication network (g) are both directed network. The communication network are also weighted network. I intend to see the whether the presence of a tie in follower-followee network in a dyad would impact the presence of a tie in their communication network. So I guest the dyadcov is the proper term to model this, right?

Everything looks fine when I put only node attribute terms (e.g. nodeicov (“fan”)) and homophilic attribute (e.g. nodematch (“location”)) and dyadcov term dyadcov(ff) into the model.

fit0.1<-ergm(g~edges

+nodeicov("follow")+nodeicov("weibo")+nodeicov("fans")

+nodematch("location")+nodematch("group")+nodematch("level")

+dyadcov(ff),

control=control.ergm(MCMC.burnin=10000,MCMC.samplesize = 5000,seed=1,MCMC.interval=10000,parallel = 4,parallel.type = "PSOCK"),

response = NULL, verbose = FALSE)

#This model was fit using MCMC. To examine model diagnostics and check for degeneracy, use the mcmc.diagnostics() function.



However, when I add an endogenous term “mutual” into the model

fit0.2<-ergm(g~edges

+nodeicov("follow")+nodeicov("weibo")+nodeicov("fans")

+nodematch("location")+nodematch("group")+nodematch("level")

+dyadcov(ff)

+mutual,

control=control.ergm(MCMC.burnin=10000,MCMC.samplesize = 5000,seed=1,MCMC.interval=10000,parallel = 4,parallel.type = "PSOCK"),

response = NULL, verbose = FALSE)

#The model was converged once after Iteration 1.

But it returns error at Iteration 2.

#Iteration 2 of at most 20:

#Optimizing with step length 1.

#Error in solve.default(H, tol = 1e-20) :

Lapack routine dgesv: system is exactly singular: U[11,11] = 0



What does this error mean? How can I solve this problem?



Actually I realize that it maybe the combination of two terms “dyadcov” and “mutual” that cause the problem, because when I replace mutual with other terms, it works fine.



With the combination of dyadcov and some other structural terms (e.g. dgwdsp, gwidegree) the model can be converged, but still I got the following warning messages:

# in term “dyadcov” in package “ergm”: asymmetric covariate in dyadcov using upper triangle only. (and the same appears repeatedly in one run)

I can see all the model coefficients are all reported in some cases, including lower triangle, but missing of lower coefficients in other cases, i.e. only upper triangle coefficients along with other coefficients are reported. Wondering why it happens?



I hope my messages won’t be too long to read .

Thank you in advance for any advice on what to look out for!



Best regards,

Dr. Pianpian Wang



Assistant Professor

School of media and communication

Shenzhen University






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