Fix issue #13

DESCRIPTION

@@ -1,6 +1,6 @@
 Package: mwcsr
 Title: Solvers for Maximum Weight Connected Subgraph Problem and Its Variants
-Version: 0.1.11
+Version: 0.1.12
 Authors@R: c(person("Alexander", "Loboda", email = "aleks.loboda@gmail.com", role = c("aut", "cre")),
     person("Nikolay", "Poperechnyi", email = "n.poperechnyi@gmail.com", role = "aut"),
     person("Eduardo", "Alvarez-Miranda", email = "ealvarez@utalca.cl", role = "aut"), 

R/rnc_sgmwcs.R

@@ -56,6 +56,7 @@ solve_mwcsp.rnc_solver <- function(solver, instance, ...) {
 
     if (length(res$edges) == 0) {
         g <- igraph::induced_subgraph(instance, vids = res$vertices)
+        g <- igraph::delete_edges(g, igraph::E(g))
     } else {
         g <- igraph::subgraph_from_edges(instance, eids = res$edges)
     }

tests/testthat/test_rnc.R

@@ -37,6 +37,16 @@ test_that("rnc solver handles non-integer signal weights in single-vertex soluti
     expect_equal(solution$weight, 2.193558)
 })
 
+test_that("rnc solver handles self-loops with negative signal weights (#13)", {
+    solver <- rnc_solver(max_iterations=50)
+    g <- igraph::make_graph(c(1, 1), directed=FALSE) # loop
+    V(g)$signal <- "s1"
+    E(g)$signal <- "s2"
+    g$signals <- c(s1=0, s2=-1)
+    solution <- solve_mwcsp(solver, g)
+    expect_equal(solution$weight, 0)
+})
+
 test_that("sgmwcs rnc solver gives good solution for a GAM instance", {
     rnc <- rnc_solver(max_iterations = 100)
     solution <- solve_mwcsp(rnc, gmwcs_example)