Number Sort Algorithm

[aratti]

Hi Darrel, I tested the sorting snippet you have posted, using a rather interesting swapping technique.

The code worked, but now and than, it was yielding very fanny results.

From a closer code analysis, I came to the conclusion that :

If CounterA > 0 then CounterA=CounterA-2

should be corrected with:

If CounterA > 1 then CounterA=CounterA-2

After the correction, I didn't see any fanny result for the rest of my testing period.

The explanation I have given is the following:

If CounterA = 1 then CounterA - 2 = 255 and this screw up everything.

Can you confirm?

Al.

[Darrel Taylor]

Hi Darrel, I tested the sorting snippet you have posted, using a rather interesting swapping technique.
The code worked, but now and than, it was yielding very fanny results.
From a closer code analysis, I came to the conclusion that :

If CounterA > 0 then CounterA=CounterA-2

should be corrected with:

If CounterA > 1 then CounterA=CounterA-2

After the correction, I didn't see any fanny result for the rest of my testing period.
The explanation I have given is the following:

If CounterA = 1 then CounterA - 2 = 255 and this screw up everything.

Can you confirm?

Al.

Well, I wouldn't think it's a problem.
Right after the IF block that statement is in, Melanie put a ...

CounterA=CounterA+1

So if CounterA = 1, subtracting 2 makes it 255, then adding 1 makes it 0 again.

Had you made any other changes?
<br>

[aratti]

Had you made any other changes?

Yes, a second one, but more for cleaning the code, since it didn't effect functionality:

RawData(CounterA+1+0) = RawData(CounterA) ^ RawData(CounterA+1)

Has been cleaned with:

RawData(CounterA+1) = RawData(CounterA) ^ RawData(CounterA+1)

Well, I wouldn't think it's a problem.
Right after the IF block that statement is in, Melanie put a ...

CounterA=CounterA+1

So if CounterA = 1, subtracting 2 makes it 255, then adding 1 makes it 0 again

But the above make sense, I do better check the whole system again.

Thank you Darrel.

Al.

[boroko]

WOW, must be a good day!
I remembered Melanie had a comment on sorting out changing inputs, but I couldn't find my bookmark for it. I went to the main forum page and there it was on the right column!
Whew! someone must be looking out for me....

My situation involves reading WORD sized data every 30ms (with quite a few spurious readings) and controlling a PWM output with somewhere near a 2-3 second response to drive some mechanicals that require slow reaction. I have been trying to mold Darrel's DT_Average16 routine to make it work, but with little success in this application.

Can someone elaborate a bit on feeding fresh data into this sort and trimming the top and bottom readings? I don't understand how to run this with a continuous data stream without blowing up the sort.

Thanks
Bo

[boroko]

Here is what I have come up with so far.....
it is getting closer.
Derived from Malanie's suggestion about parsing data and DT's averaging scheme * PIC18F2525 @ 8 MHz

ByteData var byte                                                                                                      
CounterA    var word             ' sort counter
CounterB    var byte
CounterC    var byte
DataA       var word             ' storage for sorted values
DatSort     var byte             ' pointer to middle 8 values
DatAvg      var word             ' averaged value of sorted data
RawData     var word[16]         ' storage for raw data
Clear
AvgCount	CON  8		         ' = Number of samples to average
FAspread	CON  1000	         ' = Fast Average threshold +/-
INCLUDE "AllDigital.pbp"
DEFINE OSC 8
OSCCON = %01110000
DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1
DEFINE HSER_CLROERR 1 ' Clear overflow automatically
DEFINE HSER_SPBRG 34  ' 57600 Baud @ 8MHz, -0.79%
SPBRGH = 0
BAUDCON.3 = 1         ' Enable 16 bit baudrate generator

hserout["SortAverage",10,13]
pause 500
goto Start

'Sort Array SUB ** collects 16 readings, sorts, and averages middle 8 ******
SortArray:
    CounterA=0
SortLoop:                          ' sorts 16 readings of RawData in order
    If RawData(CounterA+1) < RawData(CounterA) then
        DataA=RawData(CounterA)
        RawData(CounterA)=RawData(CounterA+1)
        RawData(CounterA+1+0)=DataA
        If CounterA > 0 then CounterA=CounterA-2
        endif
    CounterA=CounterA+1
    If CounterA < 15 then goto SortLoop
'    for CounterC = 0 to 15        ' These three lines O/P the sort results
'    hserout["Ordered[",dec CounterC,"]= ", dec RawData[CounterC],10,13] 
'    next CounterC
'**** Trim and Average ***************************************************
   for DatSort = 4 to 11                    ' pick out middle 8 readings
    IF ABS (DatAvg - RawData[DatSort]) > FAspread Then CatchUp
    IF ABS (DatAvg - RawData[DatSort]) < AvgCount Then RealClose
    DatAvg = DatAvg - (DatAvg/AvgCount)
    DatAvg = DatAvg + (RawData[DatSort]/AvgCount)
    GoTo AVGok
  CatchUp:
    DatAvg = DatAvg + (RawData[DatSort]/8)  ' catch-up by 1/8 value of reading
    GoTo AVGok
  RealClose:
    DatAvg = DatAvg - (RawData[DatSort]/(AvgCount/4))
    DatAvg = DatAvg + (DatAvg/(AvgCount/4))
  AVGok:
' hserout["Middle[",dec datsort,"] = ",dec RawData[DatSort],10,13] 'SHOW mid 8
   next DatSort
    Return  
'** END SUB************************
Start:
      FOR CounterB=0 to 15
     HSERIN [RawData[CounterB]]
      NEXT CounterB      
      FOR CounterB=0 to 15
      HSEROUT["RawData[",DEC counterB,"] = ",DEC rawdata[CounterB],10,13]
      NEXT CounterB
      CALL SortArray
      HSEROUT ["Sorted Averaged result ",dec DatAvg,10,13]
     GOTO start

[aratti]

for DatSort = 4 to 11                    ' pick out middle 8 readings
 DatAvg = DatAvg + RawData[DatSort]
NEXT DatSort

DatAvg = DatAvg >>3
Return

You can short and semplify your averaging routine with the above example. DatAvg sums up the 8 central values then you devide by 8 for the average.

Al.

[boroko]

Hi Al. Thanks for looking at it.

I like the way you simplified, but my concern was that since I will be working with WORD data, the result of the addition could get big enough that I would have to use LONGs if I didn't use DT's running average scheme.

So far, I have only tested it with byte data, and it does seem to settle slowly on something close to average. I need to try WORD data and see how that works.

Bo