--- a
+++ b/data preprocessing_Matlab/onoffset.m
@@ -0,0 +1,20 @@
+function [ ind ] = onoffset( interval,mode )
+%Function calculates on/off set of QRS complexe
+slope = [];
+for i = 2:length(interval)-1
+    slope(end+1) = interval(i+1)-interval(i-1);
+end
+%   using MIN_SLOPE determine onset placement
+if strcmp(mode,'on')
+    [m,ind] = min(abs(slope));
+    %display('onset detected');
+elseif strcmp(mode,'off')
+    slope_th = 0.2*max(abs(slope));
+    slope_s = find(abs(slope)>=slope_th);
+    ind = slope_s(1);
+else
+    display('wrong input, please select on/off set')
+end
+
+end
+