How to group a lot exponent in MQL4 / MT4?

Question

I manage to get normal lot exponent but I need to change it a bit by grouping example in the picture. Can someone guide me how to get the lot exponent but with a grouping technique Group= 5 Exponent= 1.8 ?

double GroupExponent(int type)
{
   double lot=0,exponent=1.8,group=5,initialLot=0.01;
   if(type==OP_SELL)                         
   .............                            //<---- Do i need to loop this area ?
      lot= initialLot * MathPow(exponent,TotalSell());   
   return lot;
}

int TotalSell()
{
   int Sell=0;
   for(int trade=OrdersTotal()-1; trade>=0; trade--)
   {
      if(!OrderSelect(trade,SELECT_BY_POS,MODE_TRADES))continue;
      if(OrderSymbol()==Symbol() && OrderType()==OP_SELL))
         Sell++;
   }
   return Sell;
}

Answer 1

No, you don't need a cycle. You can attain your layer system like this:

double GroupExponent(int type)
{
   double lot=0,exponent=1.8,initialLot=0.01;
   int group = 5;
   if(type==OP_SELL)                         
   {
      lot = NormalizeDouble(initialLot * MathPow(exponent, (TotalSell() - 1) / group), 2);
   }
   return lot;
}

int TotalSell()
{
   int Sell=0;
   for(int trade=OrdersTotal()-1; trade>=0; trade--)
   {
      if(!OrderSelect(trade,SELECT_BY_POS,MODE_TRADES))continue;
      if(OrderSymbol()==Symbol() && OrderType()==OP_SELL))
         Sell++;
   }
   return Sell;
}

Note: This will work as intended only if Layer == 1 equals TotalSell() == 1 . If Layer == 1 equals TotalSell() == 0 , then there is no need to subtract 1 from TotalSell() inside MathPow() .

Answer 2

Q : "How to group a lot exponent in MQL4 / MT4?"

Well, technically speaking, the Exponent = 1.8 is not an exponent per-se, but rather a scaling constant, that gets exponentiated by plain ordinals.

See the calculation formula of the Lot-sizings, that match the Table above:

|
|>>> for                                   aLayerNUMBER in range( 1, 11 ):
...      aVolumeInLOTs = 0.01 * ( 1.8 ** ( aLayerNUMBER - 1 ) )
...      print "LAYER: {0: >2d} - {1: >5.2f} Lots".format( aLayerNUMBER,
...                                                        aVolumeInLOTs
...                                                        )
... 
LAYER:  1 -  0.01 Lots
LAYER:  2 -  0.02 Lots
LAYER:  3 -  0.03 Lots
LAYER:  4 -  0.06 Lots
LAYER:  5 -  0.10 Lots
LAYER:  6 -  0.19 Lots
LAYER:  7 -  0.34 Lots
LAYER:  8 -  0.61 Lots
LAYER:  9 -  1.10 Lots
LAYER: 10 -  1.98 Lots
+0:01:07.587141
13:31:06
|
|>>>

In MQL4 there will go, most often this :
double aVolumeInLOTs = NormalizeDouble( 0.01 * MathPow( 1.8, aLayerNUMBER - 1 ), 2 );

The groupings are groups of (here) 5 trades, each having the same size / volume,
again in the exponentiated progression of ( 0.01, 0.02, 0.03, 0.06, 0.10, 0.19, 0.34, 0.61, 1.10, 1.98, 3.57, 6.42, 11.56, 20.82, 37.48, 67.46, 121.43, 218.59, 393.46, ... )

The last piece of the puzzle is a reason, where to stop producing the 5-trades' groups ( why stopping right at the fourth group-of-5-s, sized 0.06 Lots each, and not proceeding anywhere further ).

That information was not present in the Question and remains thus an un-decidable for us, obviously, unless more pieces of information were added.