<s>
In	O
statistics	O
,	O
an	O
approximate	B-Language
entropy	I-Language
(	O
ApEn	O
)	O
is	O
a	O
technique	O
used	O
to	O
quantify	O
the	O
amount	O
of	O
regularity	O
and	O
the	O
unpredictability	O
of	O
fluctuations	O
over	O
time-series	O
data	O
.	O
</s>
<s>
A	O
comprehensive	O
step-by-step	O
tutorial	O
with	O
an	O
explanation	O
of	O
the	O
theoretical	O
foundations	O
of	O
Approximate	B-Language
Entropy	I-Language
is	O
available	O
.	O
</s>
<s>
Step	O
2	O
Let	O
be	O
a	O
positive	O
integer	O
,	O
with	O
,	O
which	O
represents	O
the	O
length	O
of	O
a	O
run	O
of	O
data	O
(	O
essentially	O
a	O
window	B-Language
)	O
.Let	O
be	O
a	O
positive	O
real	O
number	O
,	O
which	O
specifies	O
a	O
filtering	O
level.Let	O
.	O
</s>
<s>
ApEn	O
has	O
been	O
applied	O
to	O
classify	O
electroencephalography	B-Application
(	O
EEG	B-Application
)	O
in	O
psychiatric	O
diseases	O
,	O
such	O
as	O
schizophrenia	O
,	O
epilepsy	O
,	O
and	O
addiction	O
.	O
</s>
