4 files changed, 18 insertions, 8 deletions
diff --git a/xtract/xtract_delta.h b/xtract/xtract_delta.h
index 9b4f28f..6e19708 100644
--- a/xtract/xtract_delta.h
+++ b/xtract/xtract_delta.h
@@ -18,7 +18,7 @@
  * USA.
  */
 
-/** \file xtract_delta.h: declares functions that extract a feature as a single value or vector from more than one input vector */
+/** \file xtract_delta.h: declares functions that scalar or vector value from 2 or more input vectors */
 
 #ifndef XTRACT_DELTA_H
 #define XTRACT_DELTA_H
@@ -27,15 +27,23 @@
 extern "C" {
 #endif
 
+/**
+  * \defgroup delta `delta' extraction functions
+  *
+  * Functions that extract a scalar or vector value from 2 or more input vectors
+  *
+  * @{
+  */
+
 #include "xtract_types.h"
 
-/* \brief Extract flux 
+/** \brief Extract flux 
  *
  * An alias for xtract_lnorm()
  */
 int xtract_flux(const float *data, const int N, const void *argv , float *result);
 
-/* \brief Extract the L-norm of a vector
+/** \brief Extract the L-norm of a vector
  *
  * \param *data: a pointer to the first element in an array of floats representing the difference between two subsequent frames of output from a vector-based feature e.g. the *result from xtract_difference_vector()
  * \param N: the length of the array pointed to by *data
@@ -67,6 +75,8 @@ int xtract_difference_vector(const float *data, const int N, const void *argv, f
 /*xtract_frame_tracker *xf */
 /*float frames*/
 
+/** @} */
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/xtract/xtract_macros.h b/xtract/xtract_macros.h
index 2eed28e..095493d 100644
--- a/xtract/xtract_macros.h
+++ b/xtract/xtract_macros.h
@@ -18,8 +18,6 @@
  * USA.
  */
 
-
-
 /** \file xtract_macros.h: defines useful public macros */
 
 #ifndef XTRACT_MACROS_H
diff --git a/xtract/xtract_scalar.h b/xtract/xtract_scalar.h
index bfac9a9..9bccb01 100644
--- a/xtract/xtract_scalar.h
+++ b/xtract/xtract_scalar.h
@@ -29,8 +29,9 @@ extern "C" {
 
 /**
   * \defgroup scalar scalar extraction functions
+  * 
+  * Functions that extract a feature as a single value from an input vector
   *
-  * Defines scalar extraction functions, and their parameters.
   * @{
   */
 
diff --git a/xtract/xtract_vector.h b/xtract/xtract_vector.h
index 1d68080..5eb663a 100644
--- a/xtract/xtract_vector.h
+++ b/xtract/xtract_vector.h
@@ -18,7 +18,7 @@
  * USA.
  */
 
-/* xtract_scalar.h: declares functions that extract a feature as a vector from an input vector */
+/** \file xtract_vector.h: declares functions that extract a feature as a vector from an input vector */
 
 #ifndef XTRACT_VECTOR_H
 #define XTRACT_VECTOR_H
@@ -30,7 +30,8 @@ extern "C" {
 /**
   * \defgroup vector vector extraction functions
   *
-  * Defines vector extraction functions, and their parameters.
+  * Functions that extract a feature as a vector from an input vector
+  *
   * @{
   */