Updated comments.

src/kernel_hydro.h

@@ -438,8 +438,7 @@ static const vector cond = FILL_VEC(0.5f);
 
 /**
  * @brief Computes the kernel function and its derivative for two particles
- * using vectors. Does not return zero if $u > \\gamma = H/h$, should only
- * be called if particles are known to interact.
+ * using vectors. The return value is undefined if $u > \\gamma = H/h$.
  *
  * @param u The ratio of the distance to the smoothing length $u = x/h$.
  * @param w (return) The value of the kernel function $W(x,h)$.
@@ -517,10 +516,8 @@ __attribute__((always_inline)) INLINE static void kernel_deval_1_vec(
 
 /**
  * @brief Computes the kernel function and its derivative for two particles
- * using interleaved vectors. Does not return zero if $u > \\gamma = H/h$,
- * should only
- * be called if particles are known to interact.
- *
+ * using interleaved vectors. The return value is undefined if $u > \\gamma = H/h$. 
+ * 
  * @param u The ratio of the distance to the smoothing length $u = x/h$.
  * @param w (return) The value of the kernel function $W(x,h)$.
  * @param dw_dx (return) The norm of the gradient of $|\\nabla W(x,h)|$.
@@ -643,8 +640,7 @@ __attribute__((always_inline)) INLINE static void kernel_deval_2_vec(
 
 /**
  * @brief Computes the kernel function for two particles
- * using vectors. Does not return zero if $u > \\gamma = H/h$, should only
- * be called if particles are known to interact.
+ * using vectors. The return value is undefined if $u > \\gamma = H/h$. 
  *
  * @param u The ratio of the distance to the smoothing length $u = x/h$.
  * @param w (return) The value of the kernel function $W(x,h)$.
@@ -704,8 +700,7 @@ __attribute__((always_inline)) INLINE static void kernel_eval_W_vec(vector *u,
 
 /**
  * @brief Computes the kernel function derivative for two particles
- * using vectors. Does not return zero if $u > \\gamma = H/h$, should only
- * be called if particles are known to interact.
+ * using vectors. The return value is undefined if $u > \\gamma = H/h$.
  *
  * @param u The ratio of the distance to the smoothing length $u = x/h$.
  * @param dw_dx (return) The norm of the gradient of $|\\nabla W(x,h)|$.