What is 'rg.sample' function and which package does it belong to?

I am learning some codes about Graph Convolutional Network(GCN) and there is a line:

A1 <- rg.sample(P1)

throwing following error:

Error in rg.sample(P1) : could not find function "rg.sample"

I can't find the corresponding package to install and i don't know what this function mean. I tried google but nothing related. Thanks for any help!