Implemented upper and lower triangle methods in NumRuby

lib/nmatrix/numruby.rb

@@ -62,4 +62,27 @@ def self.hstack(objs)
     result
   end
 
+  def self.tri(N, M=None, k=0, nm_dtype=float)
+    if M is None:
+        M = N
+
+      m = greater_equal.outer(arange(N, nm_dtype=nm_int(0, N)),
+                              arange(-k, M-k, nm_dtype=nm_int(-k, M - k)))
+
+      # Avoid making a copy if the requested type is already bool
+      m = m.stype(nm_dtype, copy=False)
+      return m
+    end
+  end
+
+  def tril(m, k=0)
+    m = Array(m)
+    mask = tri(*m.shape[-2:], k=k, nm_dtype=nm_bool)
+  end
+
+  def triu(m, k=0)
+    m = Array(m)
+    mask = tri(*m.shape[-2:], k=k-1, nm_dtype=nm_bool)
+  end
+
 end