[fpc-devel] Numeric error in the calculation of Variance

[Anton Shepelev]

Hello, all

May  I  ask you if there is any chance of fixing the
error in the Math unit that I reported here:

   https://bugs.freepascal.org/view.php?id=32804

and provided a patch?  Here is a test case:

Program Vartest;
uses Math;

const Size = 1000000;
var dataS: array of Single;
    dataD: array of Double;
    dataE: array of Extended;
    i,n: longint;
begin
  WriteLn('Each run should return a value near unity.');

  WriteLn('Single:');
  SetLength( dataS, Size );
  for n := 1 to 4 do
  begin
    for i := 0 to Size - 1 do
    begin
      dataS[i] := 10000000 + RandG(0,1);
    end;
    WriteLn( Math.Variance( dataS ):5:3 );
  end;

  WriteLn('Double:');
  SetLength( dataD, Size );
  for n := 1 to 4 do
  begin
    for i := 0 to Size - 1 do
    begin
      dataD[i] := 1000000000000000 + RandG(0,1);
    end;
    WriteLn( Math.Variance( dataD ):5:3 );
  end;

  WriteLn('Extended:');
  SetLength( dataE, Size );
  for n := 1 to 4 do
  begin
    for i := 0 to Size - 1 do
    begin
      dataE[i] := 1000000000000000000 + RandG(0,1);
    end;
    WriteLn( Math.Variance( dataE ):5:3 );
  end;
end.

-- 
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