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RE: [amibroker] Built-in DEMA questions



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I see that the 
1st line got miscopied.
Bob
<SPAN 
class=931400100-27042003> 
Len = 14; ef = 2/(Len+1);
DEMA1 = 2 * <FONT 
color=#0000ff>EMA( C, len ) - EMA( 
EMA( C, len ), Len );
DEMA2 = 2*<FONT 
color=#0000ff>AMA(C,ef) -AMA(<FONT 
color=#0000ff>AMA(C,ef),ef);

Plot<FONT color=#000080 
size=2>(1.01*DEMA(C,Len),"D",<SPAN 
class=218500120-26042003>4,4);
Plot(DEMA1,"D1",5,4);<FONT 
color=#0000ff>
Plot<FONT color=#000080 
size=2>(DEMA2,"D2",5,4);

  <FONT face=Tahoma 
  size=2>-----Original Message-----From: Bob Jagow 
  [mailto:bjagow@xxxxxxxxxxx]Sent: Saturday, April 26, 2003 2:00 
  PMTo: amibroker@xxxxxxxxxxxxxxxSubject: RE: [amibroker] 
  Built-in DEMA questions
  <FONT face=Arial color=#000080 
  size=2>Dimitris,
  <SPAN 
  class=218500120-26042003>I'd earlier noticed that EMA is 
  empty prior to Len, so was going to 
  suggest that you formulate a custom DEMA in terms of AMA, which differs from 
  EMA in starting at Bar1. 
  <SPAN 
  class=218500120-26042003><FONT 
  color=#000080>Turns out, as your 
  example shows, that DEMA has no lag; 
  this <FONT 
  color=#000080>is because 
  DEMA uses AMA [i.e., the docs are 
  wrong].
  <SPAN 
  class=218500120-26042003> 
  <SPAN 
  class=218500120-26042003>Bob
  <SPAN 
  class=218500120-26042003>-----<FONT 
  color=#000080>
  2<FONT face=Arial 
  size=2> * EMA( C, len ) - EMA( EMA( C, len ), Len 
);
  DEMA1 = 2 * 
  EMA( C, len ) - <FONT 
  color=#0000ff>EMA( EMA( C, len ), Len 
  );
  DEMA2 = 2*<FONT 
  color=#0000ff>AMA(C,ef) -AMA(<FONT 
  color=#0000ff>AMA(C,ef),ef);
  Plot<FONT face=Arial 
  size=2>(1.<SPAN 
  class=218500120-26042003>01*DEMA(C,Len),"D",<SPAN 
  class=218500120-26042003>4,4);
  <FONT face=Arial color=#000080 
  size=2>Plot(DEMA1,"D1",5,4);
  Plot<FONT face=Arial 
  size=2>(DEMA2,"D2",5,4);
   
  
    <FONT face=Tahoma 
    size=2>-----Original Message-----From: Dimitris Tsokakis 
    [mailto:TSOKAKIS@xxxxxxxxx]Sent: Saturday, April 26, 2003 5:14 
    AMTo: amibroker@xxxxxxxxxxxxxxxSubject: [amibroker] 
    Built-in DEMA questions
    Some things should be explained about DEMA and its 
    expected behavior:Let us use a fast DEMA [green line, period=10] and a 
    slow one [yellow line, period=10]A third, variable period DEMA [the 
    black thicker line], uses the fast period and, suddenly, 200 bars ago, 
    changes to slow.The result will immediately leave the green curve, but 
    asymptotically touch the yellow one. It will not be a real 50-bar DEMA, 
    even after 200 bars.Note that all this 200-bar period the variable DEMA 
    stays higher than the slow one. [above gif]To answer my [obvious] 
    questions, I search the available reference [instead of leaving my 
    imagination to fly around].The explanatory note via <A 
    href="">http://groups.yahoo.com/group/amibroker/message/38844 
    sends me to <A 
    href="">http://www.amibroker.com/guide/afl/afl_view.php?name=DEMAwhere 
    I read the comment
     
    DEMA internally is implemented via 
    EMA:Len=10;Graph0= 2 * EMA( C, len ) - EMA( EMA( C, len ), Len 
    );// for comparison onlyGraph1=DEMA(C,Len);
     
    Some more explanations should be added 
    because:a. The built-in DEMA 
    begins from the first bar and the analytic EMA equivalent begins 400 bars 
    later. How the built-in DEMA is defined for the first 400 bars ? 
    [The question holds for IB and AA, see the simple 
    exploration
     
    Len=200;G0= 2 * EMA( C, len ) - EMA( EMA( C, len ), 
    Len );G1=DEMA(C,Len);Filter=1;AddColumn(G0,"ANALYTIC 
    DEMA");AddColumn(G1,"DEMA");AddColumn(Cum(1),"BARS",1.0);
     
    and the att. gif]
     
    b. Should we 
    expect a 2*Len delayed response when variable periods is used 
    ?c. My CSCO history is 831 
    bars [Jan3, 2000 till now]. The Graph0= 2 * EMA( C, len ) - EMA( EMA( C, 
    len ), Len );begins on Aug2, 2001.c1.Can 
    we speak for a proper function use back in the critical Oct2, 2001 CSCO 
    low?The built-in DEMA is 11.53 and the EMA equivalent is 9.08 
    !!!!!c2.After how many bars the two formulas 
    are less than 1% diverging ?
     
    Built-in DEMA is, IMO, one of the most powerful AFL 
    tools, its use in trading systems design gives excellent resultsand this 
    is accurately translated to interesting profits. To avoid any 
    misunderstanding [the recent winds are S to SW, not that healthy...]my 
    questions do not search for built-in functions secrets, it would be useless 
    to me. 
    Just a better explanation to understandthe 
    expected DEMA behavior would encourage users/traders to step 
    into this great function. 5-10 lines would be more than enough, no need 
    for 1000+ pages.Thank you in advance for any reply.Dimitris 
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