Index: trunk/src/transform_field/diff_vel.m
===================================================================
--- trunk/src/transform_field/diff_vel.m	(revision 871)
+++ trunk/src/transform_field/diff_vel.m	(revision 876)
@@ -1,11 +1,11 @@
-%'sub_field': combines two input fields
+%'diff_vel': calculate the difference of two input velocity fields. 
 %
-% the two fields are subtstracted when of the same nature (scalar or
-% vector), if the coordinates do not coincide, the second field is
-% interpolated on the cooridintes of the first one
-%
-% when scalar and vectors are combined, the fields are just merged in a single matlab structure for common visualisation
+% the second velocity field is linearly interpolated 
+% (after elimination of the vectors marked with an error flag) to the positions of
+% the first one before subtraction. The ancilary data of the first field
+% are preserved while those of the second one are lost. 
+
 %-----------------------------------------------------------------------
-% function SubData=sub_field(Field,XmlData,Field_1)
+% function SubData=diff_vel(Field,XmlData,Field_1)
 %
 % OUPUT: 
@@ -14,4 +14,5 @@
 % INPUT: 
 % Field: matlab structure representing the first field
+% XmlData: not used, needed for consistency with the call of transform fct.
 % Field_1:matlab structure representing the second field
 
Index: trunk/src/transform_field/signal_spectrum.m
===================================================================
--- trunk/src/transform_field/signal_spectrum.m	(revision 871)
+++ trunk/src/transform_field/signal_spectrum.m	(revision 876)
@@ -1,3 +1,3 @@
-% 'signal_spectrum': calculate and display spectrum of the current field 
+% 'signal_spectrum': calculate and display power spectrum of the current field 
 %  operate on a 1D signal or the first dimension of a higher dimensional matrix (then average over other dimensions)
 %  this function aplies the Welch method and call the function of the matlab signal processing toolbox
Index: trunk/src/transform_field/sub_field.m
===================================================================
--- trunk/src/transform_field/sub_field.m	(revision 871)
+++ trunk/src/transform_field/sub_field.m	(revision 876)
@@ -1,7 +1,6 @@
-%'sub_field': combines two input fields
+%'sub_field': combines two input fields, taking the difference if of the same nature
 %
-% the two fields are subtstracted when of the same nature (scalar or
-% vector), if the coordinates do not coincide, the second field is
-% interpolated on the cooridintes of the first one
+% the two fields are subtracted when of the same nature (scalar or
+% vector),and defined at the same points
 %
 % when scalar and vectors are combined, the fields are just merged in a single matlab structure for common visualisation