# HG changeset patch
# User Minh Van Nguyen <nguyenminh2@gmail.com>
# Date 1305295810 25200
# Node ID 20adce9468afda8100405eb57a3e6667b0326a5b
# Parent  3ee6854bb6e85a7dee5ec6242e853ad51d37851d
vector of zeros; based on trunk #2463
The default behaviour of igraph_vector_init() is to construct a vector of
a given size and then initializes each entry to zero. Document this and
point out that one could just use igraph_vector_init() to create a vector
of zeros, rather than first construct a vector and then use
igraph_vector_null().

diff --git a/examples/simple/vector.c b/examples/simple/vector.c
--- a/examples/simple/vector.c
+++ b/examples/simple/vector.c
@@ -43,6 +43,11 @@
   igraph_vector_init(&v, 0);
   igraph_vector_destroy(&v);
 
+  /* vector of zeros */
+  igraph_vector_init(&v, 10);
+  print_vector(&v, stdout);
+  igraph_vector_destroy(&v);
+
   /* VECTOR(), igraph_vector_size */
   igraph_vector_init(&v, 10);
   for (i=0; i<igraph_vector_size(&v); i++) {
diff --git a/examples/simple/vector.out b/examples/simple/vector.out
--- a/examples/simple/vector.out
+++ b/examples/simple/vector.out
@@ -1,3 +1,4 @@
+ 0 0 0 0 0 0 0 0 0 0
  10 9 8 7 6 5 4 3 2 1
  0 100 200 300 400
  0 20 40 60 80
diff --git a/src/vector.pmt b/src/vector.pmt
--- a/src/vector.pmt
+++ b/src/vector.pmt
@@ -99,7 +99,11 @@
  * </para><para>
  * Every vector needs to be initialized before it can be used, and
  * there are a number of initialization functions or otherwise called
- * constructors. 
+ * constructors. This function constructs a vector of the given size and
+ * initializes each entry to 0. Note that \ref igraph_vector_null() can be
+ * used to set each element of a vector to zero. However, if you want a
+ * vector of zeros, it is much faster to use this function than to create a
+ * vector and then invoke \ref igraph_vector_null().
  * 
  * </para><para>
  * Every vector object initialized by this function should be
@@ -620,7 +624,8 @@
  * </para><para>
  * Note that \ref igraph_vector_init() sets the elements to zero as well, so
  * it makes no sense to call this function on a just initialized
- * vector. 
+ * vector. Thus if you want to construct a vector of zeros, then you should
+ * use \ref igraph_vector_init().
  * \param v The vector object.
  *
  * Time complexity: O(n), the size of