Matlab wavelet feature extraction help

How can we extract information from wavelet approximation and detail coeffients .for eg.i hav a voltage sag signal with start time=0.016 and end tim=0.02.How can i determine this duration from coeffients and the magnitude of the signal

my matlab code is

if true
  %

u = inline('t >= 0'); n=1:4 %waveform generation fs=250 A=0.7; t1=12; t2=24; t = 0:0.1:100 v1=sin(2*pi*(50/fs)*t);

v2=(1-A*(u(t-t1)-u(t-t2))).*sin(2*pi*(50/fs)*t); figure(1); plot(v1); title('Original signal'); Ylabel('s'); figure(2); plot(v2); title('Voltage Sag'); Ylabel('s'); [c,l]=wavedec(v2,6,'db6'); a6=wrcoef('a',c,l,'db6',6); figure(2); subplot(7,1,1); plot(a6); title('Decomposes the sixth layer with dbs=a6+d6+d5+d4+d3+d2+d1'); Ylabel('a6'); for i=1:6 decmp=wrcoef('d',c,l,'db6',7-i); subplot(7,1,i+1); plot(decmp); Ylabel(['d',num2str(7-i)]); end A = appcoef(C,L,'db6',6) end