diff --git a/src/python/handler/py_CT.cpp b/src/python/handler/py_CT.cpp
index a15826e..88df7ef 100644
--- a/src/python/handler/py_CT.cpp
+++ b/src/python/handler/py_CT.cpp
@@ -58,9 +58,10 @@ py::UniqueObj CTModelObject::getCorrelations(PyObject* topicId) const
 py::UniqueObj CTModelObject::getPriorCov() const
 {
 	auto* inst = getInst<tomoto::ICTModel>();
+	auto cov = inst->getPriorCov();
+	if (cov.empty()) return py::buildPyValue(nullptr);
 	float* ptr;
 	auto ret = py::newEmptyArray(ptr, inst->getK(), inst->getK());
-	auto cov = inst->getPriorCov();
 	memcpy(ptr, cov.data(), sizeof(float) * inst->getK() * inst->getK());
 	return ret;
 }
diff --git a/test/unit_test.py b/test/unit_test.py
index 3544cd8..fde7aa4 100644
--- a/test/unit_test.py
+++ b/test/unit_test.py
@@ -4,6 +4,22 @@
 curpath = os.path.dirname(os.path.realpath(__file__))
 print(curpath)
 
+def test_concat():
+    tokenizer = tp.utils.SimpleTokenizer()
+    corpus = tp.utils.Corpus(tokenizer=tokenizer)
+    corpus.process([
+        'a b 0 d e',
+        'a b 1 d e',
+        'a b d e 2',
+        'a b 3 d e',
+        'a b 4 d e',
+    ])
+    cands = corpus.extract_ngrams(min_cf=5, min_df=5, normalized=True, min_score=0.5)
+    print(cands)
+    corpus.concat_ngrams(cands)
+    for doc in corpus:
+        print(doc.words, doc.span)
+
 model_cases = [
     (tp.LDAModel, curpath + '/sample.txt', 0, None, {'k':40}, None),
     (tp.LLDAModel, curpath + '/sample_with_md.txt', 1, lambda x:x, {'k':5}, None),
@@ -65,6 +81,23 @@
     (tp.PTModel, curpath + '/sample.txt', 0, None, {'k':10, 'p':100}, [tp.ParallelScheme.PARTITION]),
 ]
 
+def properties(cls, inputFile, mdFields, f, kargs, ps):
+    print('Test properties')
+    tw = 0
+    print('Initialize model %s with TW=%s ...' % (str(cls), ['one', 'idf', 'pmi'][tw]))
+    mdl = cls(tw=tw, min_df=2, rm_top=2, **kargs)
+    all_attributes = [attr for attr in dir(mdl) if not attr.startswith('_')]
+    ignore_properties = {'CTModel.alpha', 'DTModel.eta'}
+    for attr in all_attributes:
+        if '{}.{}'.format(cls.__name__, attr) in ignore_properties:
+            print('Skipping property {}.{}'.format(cls.__name__, attr))
+            continue
+        try:
+            print(attr, getattr(mdl, attr), sep=': ')
+        except Exception as e:
+            print('Error accessing attribute {}: {}'.format(attr, e))
+            raise
+
 def null_doc(cls, inputFile, mdFields, f, kargs, ps):
     tw = 0
     print('Initialize model %s with TW=%s ...' % (str(cls), ['one', 'idf', 'pmi'][tw]))
@@ -648,6 +681,13 @@ def test_purge_dead_topics():
         mdl.train(100)
         print('Iteration: {}\tLog-likelihood: {}\tNum. of topics: {}\tNum. of tables: {}'.format(i, mdl.ll_per_word, mdl.live_k, mdl.num_tables))
 
+for model_case in model_cases:
+    pss = model_case[5]
+    if not pss: pss = [tp.ParallelScheme.DEFAULT]
+    for ps in pss[:1]:
+        for func in [properties]:
+            locals()['test_{}_{}_{}'.format(model_case[0].__name__, func.__name__, ps.name)] = (lambda f, mc, ps: lambda: f(*(mc + (ps,))))(func, model_case[:-1], ps)
+
 for model_case in model_cases:
     pss = model_case[5]
     if not pss: pss = [tp.ParallelScheme.COPY_MERGE, tp.ParallelScheme.PARTITION]
diff --git a/tomotopy/models.py b/tomotopy/models.py
index b1cbdcb..4f1115a 100644
--- a/tomotopy/models.py
+++ b/tomotopy/models.py
@@ -456,9 +456,9 @@ def set_word_prior(self, word, prior) -> None:
     
     @classmethod
     def _summary_extract_param_desc(cls:type):
-        doc_string = cls.__doc__ or cls.__init__.__doc__
+        doc_string = cls.__init__.__doc__
         if not doc_string: return {}
-        ps = doc_string.split('\nParameters\n')[1].split('\n')
+        ps = doc_string.split('Parameters\n')[1].split('\n')
         param_name = re.compile(r'^([a-zA-Z0-9_]+)\s*:\s*')
         directive = re.compile(r'^\s*\.\.')
         descriptive = re.compile(r'\s+([^\s].*)')
@@ -503,7 +503,10 @@ def _summary_training_info(self, file):
         print('| Log-likelihood per word: {:.5f}'.format(self.ll_per_word), file=file)
 
     def _summary_initial_params_info(self, file):
-        param_desc = self._summary_extract_param_desc()
+        try:
+            param_desc = self._summary_extract_param_desc()
+        except:
+            param_desc = {}
         if hasattr(self, 'init_params'):
             for k, v in self.init_params.items():
                 if type(v) is float: fmt = ':.5'
@@ -1390,7 +1393,7 @@ def get_topic_word_dist(self, topic_id, normalize=True) -> List[float]:
     @property
     def k_g(self) -> int:
         '''the hyperparameter k_g (read-only)'''
-        return self._k_g
+        return self._k
     
     @property
     def k_l(self) -> int:
diff --git a/tomotopy/viewer/template.html b/tomotopy/viewer/template.html
index da002e6..891ef97 100644
--- a/tomotopy/viewer/template.html
+++ b/tomotopy/viewer/template.html
@@ -444,17 +444,46 @@ <h3>{{get_topic_label(topic, prefix="Topic ", id_suffix=True)}}: <small>{{", ".j
               var category_labels = {{categorical_metadata}};
             </script>
             <script>
+              const backgroundColors = [
+                'rgba(54, 162, 235, 0.5)',
+                'rgba(255, 99, 132, 0.5)',
+                'rgba(255, 159, 64, 0.5)',
+                'rgba(255, 205, 86, 0.5)',
+                'rgba(75, 192, 192, 0.5)',
+                'rgba(153, 102, 255, 0.5)',
+                'rgba(201, 203, 207, 0.5)',
+                'rgba(255, 0, 0, 0.5)',
+                'rgba(0, 255, 0, 0.5)',
+                'rgba(0, 0, 255, 0.5)',
+              ];
+              const borderColors = [
+                'rgb(54, 162, 235)',
+                'rgb(255, 99, 132)',
+                'rgb(255, 159, 64)',
+                'rgb(255, 205, 86)',
+                'rgb(75, 192, 192)',
+                'rgb(153, 102, 255)',
+                'rgb(201, 203, 207)',
+                'rgb(255, 0, 0)',
+                'rgb(0, 255, 0)',
+                'rgb(0, 0, 255)',
+              ];
+
               var charts = [];
               for (var i in tdf_data) {
                 var data = tdf_data[i];
                 const ctx = document.getElementById('chart-' + i);
 
                 var datasets = [];
-                for (var c in category_labels) {
+                const reorder = [1, 2, 3, 4, 5, 0, 6, 7, 8, 9];
+                for (var c in reorder) {
+                  c = reorder[c];
                   datasets.push({
                     label: category_labels[c],
                     cubicInterpolationMode: 'monotone',
                     data: data[c],
+                    backgroundColor: backgroundColors[datasets.length % backgroundColors.length],
+                    borderColor: borderColors[datasets.length % borderColors.length],
                     borderWidth: 2,
                     pointStyle: false,
                     segment: {
diff --git a/tomotopy/viewer/viewer_server.py b/tomotopy/viewer/viewer_server.py
index 8f84871..7a9b2b5 100644
--- a/tomotopy/viewer/viewer_server.py
+++ b/tomotopy/viewer/viewer_server.py
@@ -191,11 +191,12 @@ def __init__(self, model, max_cache_size=5) -> None:
         self._cached = {}
         self._cached_keys = []
     
-    def _sort_and_filter(self, sort_key:int, filter_target:int, filter_value:float, filter_keyword:tuple, filter_metadata:str):
+    def _sort_and_filter(self, sort_key:int, filter_target:int, filter_value:float, filter_keyword:tuple, filter_metadata:str, filter_numeric_metadata:list):
         results = []
         for i, doc in enumerate(self.model.docs):
             if filter_keyword and not all(kw in doc.raw.lower() for kw in filter_keyword): continue
             if filter_metadata is not None and doc.metadata != filter_metadata: continue
+            if filter_numeric_metadata and not all(s <= v <= e for (s, e), v in zip(filter_numeric_metadata, doc.numeric_metadata)): continue
             dist = doc.get_topic_dist()
             if dist[filter_target] < filter_value: continue
             if sort_key >= 0:
@@ -208,25 +209,25 @@ def _sort_and_filter(self, sort_key:int, filter_target:int, filter_value:float,
         else:
             return [i for _, i in sorted(results, reverse=True)]
 
-    def _get_cached_filter_result(self, sort_key:int, filter_target:int, filter_value:float, filter_keyword:str, filter_metadata:str):
+    def _get_cached_filter_result(self, sort_key:int, filter_target:int, filter_value:float, filter_keyword:str, filter_metadata:str, filter_numeric_metadata:list):
         filter_keyword = tuple(filter_keyword.lower().split())
-        if sort_key < 0 and filter_value <= 0 and not filter_keyword and filter_metadata is None:
+        if sort_key < 0 and filter_value <= 0 and not filter_keyword and filter_metadata is None and not filter_numeric_metadata:
             # return None for no filtering nor sorting
             return None
-        key = (sort_key, filter_target, filter_value, filter_keyword, filter_metadata)
+        key = (sort_key, filter_target, filter_value, filter_keyword, filter_metadata, tuple(filter_numeric_metadata))
         if key in self._cached:
             return self._cached[key]
         else:
-            result = self._sort_and_filter(sort_key, filter_target, filter_value, filter_keyword, filter_metadata)
+            result = self._sort_and_filter(sort_key, filter_target, filter_value, filter_keyword, filter_metadata, filter_numeric_metadata)
             if len(self._cached_keys) >= self.max_cache_size:
                 del self._cached[self._cached_keys.pop(0)]
             self._cached[key] = result
             self._cached_keys.append(key)
             return result
 
-    def get(self, sort_key:int, filter_target:int, filter_value:float, filter_keyword:str, filter_metadata:str, index:slice):
+    def get(self, sort_key:int, filter_target:int, filter_value:float, filter_keyword:str, filter_metadata:str, filter_numeric_metadata:list, index:slice):
         # return (doc_indices, total_docs_filtered)
-        result = self._get_cached_filter_result(sort_key, filter_target, filter_value, filter_keyword, filter_metadata)
+        result = self._get_cached_filter_result(sort_key, filter_target, filter_value, filter_keyword, filter_metadata, filter_numeric_metadata)
         if result is None:
             return list(range(index.start, min(index.stop, len(self.model.docs)))), len(self.model.docs)
         else:
@@ -431,6 +432,7 @@ def get_document(self):
         filter_value = float(self.arguments.get('v', '0'))
         filter_keyword = self.arguments.get('sq', '')
         filter_metadata = int(self.arguments.get('m', '-1'))
+        filter_numeric_metadata = self.arguments.get('x', '')
         page = int(self.arguments.get('p', '0'))
         
         if not self.available.get('metadata') or filter_metadata < 0:
@@ -439,12 +441,19 @@ def get_document(self):
         else:
             md = self.model.metadata_dict[filter_metadata]
 
+        if not self.available.get('metadata') or not filter_numeric_metadata:
+            filter_numeric_metadata = []
+        else:
+            filter_numeric_metadata = list(map(float, filter_numeric_metadata.split(',')))
+            filter_numeric_metadata = list(zip(filter_numeric_metadata[::2], filter_numeric_metadata[1::2]))
+
         doc_indices, filtered_docs = self.server.filter.get(
             sort_key, 
             filter_target, 
             filter_value / 100, 
             filter_keyword,
             md,
+            filter_numeric_metadata,
             slice(page * self.num_docs_per_page, (page + 1) * self.num_docs_per_page)
         )
         total_pages = (filtered_docs + self.num_docs_per_page - 1) // self.num_docs_per_page
@@ -459,7 +468,7 @@ def get_document(self):
         self.render(action='document',
                     page=page,
                     total_pages=total_pages,
-                    filtered_docs=filtered_docs if filter_value > 0 or filter_keyword or filter_metadata >= 0 else None,
+                    filtered_docs=filtered_docs if filter_value > 0 or filter_keyword or filter_metadata >= 0 or filter_numeric_metadata else None,
                     total_docs=total_docs,
                     documents=documents,
                     sort_key=sort_key,
@@ -800,6 +809,27 @@ def cache_tdf_map_img(self, topic_id, x, y, w, h, r, contour_interval, smooth):
             contour_map[:-int(h * 0.32)] = 0
             contour_map[:-int(h * 0.16), is_sub_grid] = 0
             contour_map = contour_map.clip(0, 1)
+        else:
+            grid_map = np.zeros_like(contour_map)
+            for i in range(5):
+                t = (h * i) // 4
+                bold = i % 2 == 0
+                if t < h:
+                    grid_map[t] = 0.8 if bold else 0.5
+                if t > 0:
+                    grid_map[t - 1] = 0.8 if bold else 0.5
+                if t + 1 < h and bold:
+                    grid_map[t + 1] = 0.8 if bold else 0.5
+            for i in range(24):
+                t = (w * i) // 23
+                bold = i % 5 == 4
+                if t < w:
+                    grid_map[:, t] = 0.8 if bold else 0.5
+                if t > 0:
+                    grid_map[:, t - 1] = 0.8 if bold else 0.5
+                if t + 1 < h and bold:
+                    grid_map[:, t + 1] = 0.8 if bold else 0.5
+            colorized = colorized * (1 - grid_map[..., None]) + 0.85 * grid_map[..., None]
         colorized *= 1 - contour_map[..., None]
         img = Image.fromarray((colorized * 255).astype(np.uint8), 'RGB')
         img_buf = io.BytesIO()