What is the Delphi/Pascal equivalent to MS-Excel's NormDist function?-CodePudding

I am porting a liquid chromatography simulator from MS-Excel (it works well) to Delphi so I can have an executable I can share with students and working chromatographers. The NormDist function is central to that task. It seems that there is no Normal Distribution function (NormDist) native to Delphi.

Can anyone point me in the right direction?

CodePudding user response：

Since I'm not that deep into mathematics I simply used the keywords NormDist Excel Delphi on a search engine, which led me to this unit having exactly the same function with the same parameters as in Excel. Better download all the units, since at least 2 others are needed.

An amalgamation of all needed code would be:

const
  sqrt2pi = 2.5066282746310005; {sqrt(2*pi)}

function Erfc(X : Single) : Single;
var
  t, z, ans : Double;
begin
  z := abs(X);
  t := 1.0/(1.0 0.5*z);
  ans := t*exp(-z*z-1.26551223 t*(1.00002368 t*(0.37409196 t*(0.09678418 
    t*(-0.18628806 t*(0.27886807 t*(-1.13520398 t*(1.48851587 
    t*(-0.82215223 t*0.17087277)))))))));
  if (X >= 0.0) then
    Result := ans
  else
    Result := 2.0-ans;
end;

function NormSDist(Z : Single) : Single;
const
  sqrt2 = 1.41421356237310;
begin
  Result := 1.0-0.5*Erfc(Z/sqrt2);
end;

function NormDist(X, Mean, StandardDev : Single;
  Cumulative : Boolean) : Single;
var
  Z : Extended;
begin
  if (StandardDev <= 0) then
    raise Exception.Create('Invalid parameter');
  Z := (X-Mean)/StandardDev;
  if (Cumulative) then
    Result := NormSDist(Z)
  else
    Result := exp(-Z*Z/2.0)/(StandardDev*sqrt2pi);
end;

CodePudding user response：

Also, http://www.lohninger.com/sdlindex.html has a stat package that has often provided me with what I need.