! Copyright (C) 2008 John Benediktsson
! See http://factorcode.org/license.txt for BSD license
-USING: arrays kernel grouping math math.statistics sequences ;
+USING: arrays assocs fry kernel grouping math math.statistics math.vectors sequences ;
IN: math.finance
: enumerate ( seq -- newseq )
- #! Returns a sequence where each element and its index
- -1 swap [ [ 1+ ] dip swap [ 2array ] keep swap ] { } map-as swap drop ;
+ <enum> >alist ;
+
+<PRIVATE
+
+: weighted ( x y a -- z )
+ tuck [ * ] [ 1 swap - * ] 2bi* + ;
+
+: a ( n -- a )
+ 1 + 2 swap / ;
+
+: first-rest ( seq -- first rest )
+ [ first ] keep 1 tail-slice ;
+
+PRIVATE>
: ema ( seq n -- newseq )
- #! An exponentially-weighted moving average:
- #! A = 2.0 / (N + 1)
- #! EMA[t] = (A * VAL[t]) + ((1-A) * EMA[t-1])
- 1+ 2.0 swap / dup 1 swap - swap rot
- [ [ dup ] dip * ] map swap drop 0 swap
- [ [ dup ] 2dip [ * ] dip + dup ] map
- [ drop drop ] dip 1 tail-slice >array ;
+ a swap first-rest swap '[ [ dup ] 2dip swap rot weighted ] accumulate 2nip ;
: sma ( seq n -- newseq )
- #! Simple moving average
clump [ mean ] map ;
: macd ( seq n1 n2 -- newseq )
- #! Moving Average Convergence Divergence
- #! MACD[t] = EMA2[t] - EMA1[t]
- rot dup ema [ swap ema ] dip [ - ] 2map ;
+ rot dup ema [ swap ema ] dip v- ;
: momentum ( seq n -- newseq )
- #! Momentum
- #! M[t] = P[t] - P[t-n]
2dup tail-slice -rot swap [ length ] keep
- [ - neg ] dip swap head-slice [ - ] 2map ;
+ [ - neg ] dip swap head-slice v- ;