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context("Eigenproblems")
test_that("spectrum works for symmetric matrices", {
library(igraph)
set.seed(42)
std <- function(x) {
x <- zapsmall(x)
apply(x, 2, function(col) {
if (any(col < 0) && col[which(col != 0)[1]] < 0) { -col } else { col }
})
}
g <- sample_gnp(50, 5/50)
e0 <- eigen(as_adj(g, sparse=FALSE))
e1 <- spectrum(g, which=list(howmany=4, pos="LA"))
expect_that(e0$values[1:4], equals(e1$values))
expect_that(std(e0$vectors[,1:4]), equals(std(e1$vectors)))
e2 <- spectrum(g, which=list(howmany=4, pos="SA"))
expect_that(e0$values[50:47], equals(e2$values))
expect_that(std(e0$vectors[,50:47]), equals(std(e2$vectors)))
})
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