tEdgeFormation and tEdgeDissolution fractions are not correct

[martinamorris]

I'm pretty sure the hand calc below is right, but it doesn't match the tsna calc

library(tergm) 
#> Loading required package: network
#> 
#> 'network' 1.17.1 (2021-06-12), part of the Statnet Project
#> * 'news(package="network")' for changes since last version
#> * 'citation("network")' for citation information
#> * 'https://statnet.org' for help, support, and other information
#> 
#> 'ergm' 4.0.1 (2021-06-20), part of the Statnet Project
#> * 'news(package="ergm")' for changes since last version
#> * 'citation("ergm")' for citation information
#> * 'https://statnet.org' for help, support, and other information
#> 'ergm' 4 is a major update that introduces some backwards-incompatible
#> changes. Please type 'news(package="ergm")' for a list of major
#> changes.
library(tsna)
#> Loading required package: networkDynamic
#> 
#> 'networkDynamic' 0.11.0 (2021-06-12), part of the Statnet Project
#> * 'news(package="networkDynamic")' for changes since last version
#> * 'citation("networkDynamic")' for citation information
#> * 'https://statnet.org' for help, support, and other information
data(samplk)
samp.dyn <- networkDynamic(network.list = list(samplk1,samplk2), start=1)
#> Onsets and termini not specified, assuming each network in network.list should have a discrete spell of length 1
#> Argument base.net not specified, using first element of network.list instead
#> Created net.obs.period to describe network
#>  Network observation period info:
#>   Number of observation spells: 1 
#>   Maximal time range observed: 1 until 3 
#>   Temporal mode: discrete 
#>   Time unit: step 
#>   Suggested time increment: 1
dyads = network.dyadcount(samplk1)
edges1 = network.edgecount(samplk1)
form = tEdgeFormation(samp.dyn, start=2, end=2)
diss = tEdgeDissolution(samp.dyn, start=2, end=2)

# formation prob?
form/(dyads - edges1)
#> Time Series:
#> Start = 2 
#> End = 2 
#> Frequency = 1 
#> [1] 0.0876494
tEdgeFormation(samp.dyn, start=2, end=2, result.type="fraction")
#> Time Series:
#> Start = 2 
#> End = 2 
#> Frequency = 1 
#> [1] 0.08118081

# dissolution prob?
diss/(edges1)
#> Time Series:
#> Start = 2 
#> End = 2 
#> Frequency = 1 
#> [1] 0.3636364
tEdgeDissolution(samp.dyn, start=2, end=2, result.type="fraction")
#> Time Series:
#> Start = 2 
#> End = 2 
#> Frequency = 1 
#> [1] 0.2597403

Created on 2021-06-26 by the reprex package (v2.0.0)