enum: a pedestrian enumerator

To create an enumerating vector from a list of terminators.

ENUM creates an enumerating vector from a list of terminators N(1:n)

E = [ 1:N(1) 1:N(2) ... 1:N(x) ... 1:N(n) ]

non-integer (non-enumerable) terminators such as <inf>s or <nan>s are handled by an option

EXAMPLES
n=[nan 2 inf 3 0 0 1 3 nan]
e=enum(n)
% e = 1 2 1 2 3 1 1 2 3

e=enum(n,'-')
% e = NaN 1 2 Inf 1 2 3 0 0 1 1 2 3 NaN

e=enum(n,-100)
% e = -100 1 2 -100 1 2 3 -100 -100 1 1 2 3 -100

NOTE
this function is based on a smart snippet provided
by long-time CSSMer <STEVE AMPHLETT> in the thread
'Replicating Rows based on an Index in the Matrix'
(2005-05-01 05:18:30 EST)

see
help enum
for more explanations