diff --git a/gemma/ops.h b/gemma/ops.h
index 8cac3f9..ed12ef4 100644
--- a/gemma/ops.h
+++ b/gemma/ops.h
@@ -685,6 +685,28 @@ static HWY_NOINLINE HWY_MAYBE_UNUSED void AddAbsolutePositionalEmbeddings(
   }
 }
 
+/* RoPE as in Rotary Position Embeddings from the RoFormer paper
+   (https://arxiv.org/abs/2104.09864v5). The query and key vectors are rotated
+   as a function of their absolute position using the rotation matrix R before
+   the self-attention operation. R is a d x d matrix.
+
+   R = cos(m*theta_1) -sin(m*theta_1) ...  0              0
+       sin(m*theta_1)  cos(m*theta_1)
+            0               0         ...  0              0
+            0               0         ...  0              0
+           ...
+            0               0         ...  cos(m*theta_{d/2}) sin(m*theta_{d/2})
+            0               0         ...  sin(m*theta_{d/2}) cos(m*theta_{d/2})
+
+  Here theta_i = 10000^(-2(i-1)/d), where d is the dimension of the vector and
+  i is the ith index of the vector.
+
+  Applying the rotation matrix R to a vector v is equivalent to rotating every
+  consecutive pair of dimensions of v i.e. v_{2i} and v_{2i+1} by an angle
+  m*theta_i. However in the Gemma implementation we choose to rotate
+  the pairs of dimensions v_{i} and v_{i + d//2} instead.
+*/
+
 static HWY_NOINLINE HWY_MAYBE_UNUSED void Rope(float* HWY_RESTRICT x,
                                                size_t dim_qkv, size_t pos) {
   HWY_DASSERT(dim_qkv % 2 == 0);