Registered: May 2011
Posts: 238

code:

/*
  avgx.cpp
  
  A utility function for calculating flexible "averaging down" and "averaging up" 
  using an analytical method, ie. using a formula instead of a costly iterative method.
  
  Written by: mutluit at tinystockexchange.com
  
  2012-10-27-Sa
  
  Platform: every modern C++ compiler should compile this. Tested with g++ on Debian GNU/Linux
  
  Compile: g++ -o avgx.exe avgx.cpp
 
  The math:
    pps = (a*b + c*d) / (a+c)           # a=qty1, b=price1, c=qty2, d=price2, pps=price per share
    pl% = ((a+c)*d / (a*b + c*d) - 1.0) * 100 * (fShort ? -1.0 : 1.0)
    --> (using solver at www.quickmath.com):
      #c = -(a*b*p - 100*a*d + 100*a*b) / (d*p)
       c = -(a*b*p + (100*a*b - 100*a*d) * (fShort ? -1.0 : 1.0)) / (d*p)
       d = -(a*b*p + 100*a*b * (fShort ? -1.0 : 1.0)) / (c*p - 100*a * (fShort ? -1.0 : 1.0))
       
  Beware: 
    there is intentionally no plausibility of the user parameters built-in, ie. garbage in will give garbage out,
    so test it throughly, if necessary add your own plausibility checks.


  Examples:
      ./avgx.exe
    gives
      usage: avgx.exe curqty pricebought lastprice fShort wantPLpct  

      ./avgx.exe 1000 100 90 0 -5
    gives:
      PLpct=-10.00 AddQty=1111.11 PLpctNew=-5.00 pps=94.7368

      ./avgx.exe 1000 100 110 1 -5
    gives
      PLpct=-10.00 AddQty=909.09 PLpctNew=-5.00 pps=104.7619


    But the following parameter set will give, in the context of financial instruments, a nonsensical result,
    although the method is correct, but the input is wrong:
      ./avgx.exe 1000 100 110 0 -5
    gives
      PLpct=10.00 AddQty=-2727.27 PLpctNew=-5.00 pps=115.7895
*/

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <algorithm>
using namespace std;

int avgx(const double AdbQty0, const double AdbPrice0, const double AdbPrice, const bool AfShort, const double AdbWantPLpct)
  { // rc: 0=ok
    const double& a = AdbQty0;
    const double& b = AdbPrice0;
    const double& d = AdbPrice;
    const double& p = AdbWantPLpct;

    double c = 0;
    const double  plpct1 = ((a+c)*d / (a*b + c*d) - 1.0) * 100 * (AfShort ? -1.0 : 1.0);
    
    c                    = -(a*b*p + (100*a*b - 100*a*d) * (AfShort ? -1.0 : 1.0)) / (d*p);
    const double  plpct2 = ((a+c)*d / (a*b + c*d) - 1.0) * 100 * (AfShort ? -1.0 : 1.0);

    const double  pps    = (a*b + c*d) / (a+c);
    
    printf("PLpct=%.2lf AddQty=%.2lf PLpctNew=%.2lf pps=%.4lf\n", plpct1, c, plpct2, pps);
    
    return 0;
  }

int main(int argc, char* argv[])
  { // rc: 0=ok
    if (argc < 6)
      {
        printf("usage: avgx.exe curqty pricebought lastprice fShort wantPLpct\n");
        return 1;
      }
    int ixArg = 0;  
    const double AdbQty0      = atof(argv[++ixArg]);
    const double AdbPrice0    = atof(argv[++ixArg]);
    const double AdbPrice     = atof(argv[++ixArg]);
    const bool   AfShort      = !!atoi(argv[++ixArg]);
    const double AdbWantPLpct = atof(argv[++ixArg]);
    
    return avgx(AdbQty0, AdbPrice0, AdbPrice, AfShort, AdbWantPLpct);
  }

Registered: Aug 2012
Posts: 676

I would like to understand this, is there an English explanation ?

Registered: May 2011
Posts: 238

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Quote from Daring:
I would like to understand this, is there an English explanation ?

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Registered: May 2012
Posts: 336

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Quote from mutluit:

It's a little commandline program written in the programming language C++, with comments at the beginning.
It simply calculates how many shares one needs to buy additionally to average down the loss to a desired percent value.
There are some examples given in the comment section of the code.
One needs a C++ compiler to generate the executable program.
Under the Linux operating system such tools like compiler etc. are usually included,
under Windows you would need to install a C++ compiler first, there are some free available, for example in cygwin, mingw etc. --> just google.

Since the algorithm (the formula) is given, it should be easy to use it in a spreadsheet application like Microsoft Excel or OpenOffice Calc etc.
It's basically this line:
c = -(a*b*p + (100*a*b - 100*a*d) * (fShort ? -1.0 : 1.0)) / (d*p)

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Registered: May 2011
Posts: 238

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Quote from 2rosy:
you made something simple into something complex. no one is going to compile a little c++ formula to get answer. They wont compile anything.
MAKE IT EASY

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