2 files changed, 34 insertions, 0 deletions
diff --git a/libcrystfel/src/integer_matrix.c b/libcrystfel/src/integer_matrix.c
index f975fa8b..c8849dda 100644
--- a/libcrystfel/src/integer_matrix.c
+++ b/libcrystfel/src/integer_matrix.c
@@ -375,3 +375,34 @@ void intmat_print(const IntegerMatrix *m)
 		fprintf(stderr, "]\n");
 	}
 }
+
+
+/**
+ * intmat_is_identity
+ * @m: An %IntegerMatrix
+ *
+ * Returns true if @m is an identity matrix.
+ *
+ */
+int intmat_is_identity(const IntegerMatrix *m)
+{
+	int i, j;
+
+	for ( i=0; i<m->rows; i++ ) {
+	for ( j=0; j<m->cols; j++ ) {
+
+		signed int v;
+
+		v = intmat_get(m, i, j);
+
+		if ( i == j ) {
+			if ( v != 1 ) return 0;
+		} else {
+			if ( v != 0 ) return 0;
+		}
+
+	}
+	}
+
+	return 1;
+}
diff --git a/libcrystfel/src/integer_matrix.h b/libcrystfel/src/integer_matrix.h
index 1c930720..f413573a 100644
--- a/libcrystfel/src/integer_matrix.h
+++ b/libcrystfel/src/integer_matrix.h
@@ -65,6 +65,9 @@ extern IntegerMatrix *intmat_inverse(const IntegerMatrix *m);
 /* Determinant */
 extern signed int intmat_det(const IntegerMatrix *m);
 
+/* Is identity? */
+extern int intmat_is_identity(const IntegerMatrix *m);
+
 /* Diagnostics */
 extern void intmat_print(const IntegerMatrix *m);