From 82ae0208ca215c13047f92a96231456cf94149d0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Szabolcs=20Horva=CC=81t?= <szhorvat@gmail.com>
Date: Sat, 17 Aug 2024 16:43:42 +0000
Subject: [PATCH] feat: feedback_vertex_set()

---
 src/_igraph/convert.c     | 13 +++++++++
 src/_igraph/convert.h     |  1 +
 src/_igraph/graphobject.c | 59 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 73 insertions(+)

diff --git a/src/_igraph/convert.c b/src/_igraph/convert.c
index 3529d6921..a96bc514d 100644
--- a/src/_igraph/convert.c
+++ b/src/_igraph/convert.c
@@ -603,6 +603,19 @@ int igraphmodule_PyObject_to_fas_algorithm_t(PyObject *o,
   TRANSLATE_ENUM_WITH(fas_algorithm_tt);
 }
 
+/**
+ * \ingroup python_interface_conversion
+ * \brief Converts a Python object to an igraph \c igraph_fvs_algorithm_t
+ */
+int igraphmodule_PyObject_to_fvs_algorithm_t(PyObject *o,
+  igraph_fas_algorithm_t *result) {
+  static igraphmodule_enum_translation_table_entry_t fvs_algorithm_tt[] = {
+        {"ip", IGRAPH_FVS_EXACT_IP},
+        {0,0}
+    };
+  TRANSLATE_ENUM_WITH(fvs_algorithm_tt);
+}
+
 /**
  * \ingroup python_interface_conversion
  * \brief Converts a Python object to an igraph \c igraph_get_adjacency_t
diff --git a/src/_igraph/convert.h b/src/_igraph/convert.h
index 54094684c..22f28eb75 100644
--- a/src/_igraph/convert.h
+++ b/src/_igraph/convert.h
@@ -72,6 +72,7 @@ int igraphmodule_PyObject_to_community_comparison_t(PyObject *obj,
 int igraphmodule_PyObject_to_connectedness_t(PyObject *o, igraph_connectedness_t *result);
 int igraphmodule_PyObject_to_degseq_t(PyObject *o, igraph_degseq_t *result);
 int igraphmodule_PyObject_to_fas_algorithm_t(PyObject *o, igraph_fas_algorithm_t *result);
+int igraphmodule_PyObject_to_fvs_algorithm_t(PyObject *o, igraph_fas_algorithm_t *result);
 int igraphmodule_PyObject_to_get_adjacency_t(PyObject *o, igraph_get_adjacency_t *result);
 int igraphmodule_PyObject_to_laplacian_normalization_t(PyObject *o, igraph_laplacian_normalization_t *result);
 int igraphmodule_PyObject_to_layout_grid_t(PyObject *o, igraph_layout_grid_t *result);
diff --git a/src/_igraph/graphobject.c b/src/_igraph/graphobject.c
index 9d696c905..bdcfd3d8c 100644
--- a/src/_igraph/graphobject.c
+++ b/src/_igraph/graphobject.c
@@ -5558,6 +5558,48 @@ PyObject *igraphmodule_Graph_feedback_arc_set(
 }
 
 
+/** \ingroup python_interface_graph
+ * \brief Calculates a feedback vertex set for a graph
+ * \return a list containing the indices in the chosen feedback vertex set
+ * \sa igraph_feedback_vertex_set
+ */
+PyObject *igraphmodule_Graph_feedback_vertex_set(
+    igraphmodule_GraphObject *self, PyObject *args, PyObject *kwds) {
+  static char *kwlist[] = { "weights", "method", NULL };
+  igraph_vector_t* weights = 0;
+  igraph_vector_int_t res;
+  igraph_fvs_algorithm_t algo = IGRAPH_FVS_EXACT_IP;
+  PyObject *weights_o = Py_None, *result_o = NULL, *algo_o = NULL;
+
+  if (!PyArg_ParseTupleAndKeywords(args, kwds, "|OO", kwlist, &weights_o, &algo_o))
+    return NULL;
+
+  if (igraphmodule_PyObject_to_fvs_algorithm_t(algo_o, &algo))
+    return NULL;
+
+  if (igraphmodule_attrib_to_vector_t(weights_o, self, &weights,
+    ATTRIBUTE_TYPE_VERTEX))
+    return NULL;
+
+  if (igraph_vector_int_init(&res, 0)) {
+    if (weights) { igraph_vector_destroy(weights); free(weights); }
+  }
+
+  if (igraph_feedback_vertex_set(&self->g, &res, weights, algo)) {
+    if (weights) { igraph_vector_destroy(weights); free(weights); }
+    igraph_vector_int_destroy(&res);
+    return NULL;
+  }
+
+  if (weights) { igraph_vector_destroy(weights); free(weights); }
+
+  result_o = igraphmodule_vector_int_t_to_PyList(&res);
+  igraph_vector_int_destroy(&res);
+
+  return result_o;
+}
+
+
 /** \ingroup python_interface_graph
  * \brief Calculates a single shortest path between a source and a target vertex
  * \return a list containing a single shortest path from the source to the target
@@ -15451,6 +15493,23 @@ struct PyMethodDef igraphmodule_Graph_methods[] = {
    "@return: the IDs of the edges to be removed, in a list.\n\n"
   },
 
+  /* interface to igraph_feedback_vertex_set */
+  {"feedback_vertex_set", (PyCFunction) igraphmodule_Graph_feedback_vertex_set,
+   METH_VARARGS | METH_KEYWORDS,
+   "feedback_vertex_set(weights=None, method=\"ip\")\n--\n\n"
+   "Calculates a minimum feedback vertex set.\n\n"
+   "A feedback vertex set is a set of edges whose removal makes the graph acyclic.\n"
+   "Finding a minimum feedback vertex set is an NP-hard problem both in directed\n"
+   "and undirected graphs.\n\n"
+   "@param weights: vertex weights to be used. Can be a sequence or iterable or\n"
+   "  even a vertex attribute name. When given, the algorithm will strive to\n"
+   "  remove lightweight vertices in order to minimize the total weight of the\n"
+   "  feedback vertex set.\n"
+   "@param method: the algorithm to use. C{\"ip\"} uses an exact integer programming\n"
+   "  approach, and is currently the only available method.\n"
+   "@return: the IDs of the vertices to be removed, in a list.\n\n"
+  },
+
   /* interface to igraph_get_shortest_path */
   {"get_shortest_path", (PyCFunction) igraphmodule_Graph_get_shortest_path,
    METH_VARARGS | METH_KEYWORDS,