More PG checking

2 files changed, 26 insertions, 2 deletions

diff --git a/src/symmetry.c b/src/symmetry.c
index b0e430b5..6c290756 100644
--- a/src/symmetry.c
+++ b/src/symmetry.c
@@ -405,8 +405,9 @@ static SymOpList *make_4m()
 static SymOpList *make_4()
 {
 	SymOpList *new = new_symoplist();
-	add_symop(new, v(0,1,0,0), v(1,0,0,0), v(0,0,0,1), 4); /* 4 */
-	return NULL;
+	add_symop(new, v(0,-1,0,0), v(1,0,0,0), v(0,0,0,1), 4); /* 4 */
+	new->name = strdup("4");
+	return expand_ops(new);
 }
 
 
@@ -673,6 +674,28 @@ void get_asymm(const SymOpList *ops,
 }
 
 
+static int is_inversion(const struct sym_op *op)
+{
+	if ( (op->h[0]!=-1) || (op->h[1]!=0) || (op->h[2]!=0) ) return 0;
+	if ( (op->k[0]!=0) || (op->k[1]!=-1) || (op->k[2]!=0) ) return 0;
+	if ( (op->l[0]!=0) || (op->l[1]!=0) || (op->l[2]!=-1) ) return 0;
+	return 1;
+}
+
+
+int is_centrosymmetric(const SymOpList *s)
+{
+	int i, n;
+
+	n = num_ops(s);
+	for ( i=0; i<n; i++ ) {
+		if ( is_inversion(&s->ops[i]) ) return 1;
+	}
+
+	return 0;
+}
+
+
 /**
  * get_twins:
  *
diff --git a/src/symmetry.h b/src/symmetry.h
index 45ffe318..4ecf11a4 100644
--- a/src/symmetry.h
+++ b/src/symmetry.h
@@ -48,6 +48,7 @@ extern void get_equiv(const SymOpList *ops, const SymOpMask *m, int idx,
                       signed int h, signed int k, signed int l,
                       signed int *he, signed int *ke, signed int *le);
 
+extern int is_centrosymmetric(const SymOpList *s);
 extern SymOpList *get_twins(const SymOpList *source, const SymOpList *target);
 
 #endif	/* SYMMETRY_H */