update L1Regularizer annotation

mindspore/nn/layer/basic.py

@@ -37,11 +37,14 @@ __all__ = ['Dropout', 'Flatten', 'Dense', 'ClipByNorm', 'Norm', 'OneHot', 'Pad',
 
 
 class L1Regularizer(Cell):
-    """
+    r"""
     Apply l1 regularization to weights
 
     l1 regularization makes weights sparsity
 
+    .. math::
+        \text{loss}=\lambda * \text{reduce_sum}(\text{abs}(\omega))
+
     Note:
         scale(regularization factor) should be a number which greater than 0