function Mathlog

I'm guessing you have an array out of range error in your log? You do not SetIndexBuffer for A[].

 I suspect you'll also have problems with your color assignment (indicator_color2 Red)

And possibly also your indicator minimum (indicator_minimum    0) .... natural log of values >0  && <1 are negative (think USDCHF, for example).

The problem is that you have declared an array A[] but it has no size.

So when you access A[i] it is going to be out of range. Have you checked your Experts Tab?

Why don't you dispense with A altogether:

 

#property copyright "Copyright 2014, MetaQuotes Software Corp."
#property link      "https://www.mql5.com"
#property version   "1.00"
#property strict
#property indicator_separate_window
//#property indicator_buffers 2
#property indicator_buffers 1
//#property indicator_color2 Red
#property indicator_color1 Red
//#property indicator_minimum    -1
//#property indicator_maximum    1
double A[];
//double B[];



//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
int init()
  {
//---- indicators
//   SetIndexBuffer(0,B);
//   SetIndexStyle(0,DRAW_LINE,STYLE_SOLID,indicator_color2);
   SetIndexBuffer(0,A);
   SetIndexStyle(0,DRAW_LINE,STYLE_SOLID);
 
    return(0);
  }
//+------------------------------------------------------------------+
//| Custom indicator iteration function                              |
//+------------------------------------------------------------------+

int start()
  {
 int counted_bars=IndicatorCounted();


if (counted_bars>0)
counted_bars--;
int limit= Bars-counted_bars;


for (int i=0;i<limit;i++)
{
//----
  
  
//     A[i]=(High[i]);
//     B[i]=MathLog(A[i]);
     A[i]=MathLog(High[i]);
   
   }
   return(0);
} 

  
//+------------------------------------------------------------------+

I believe you meant dispense with B altogether right ?
As you have done in the corrected code with //B's related commenting ?

Dispense with either because only 1 is necessary.

But you are quite right though, because of my code I should have written B not A. 

The values of A are stored as doubles, so their representation accuracy is 15 significant digits. You can see this by printing the values of A.

int start()
  {
 int counted_bars=IndicatorCounted();


if (counted_bars>0)
counted_bars--;
int limit= Bars-counted_bars;


for (int i=0;i<limit;i++)
{
//----
  
  
//     A[i]=(High[i]);
//     B[i]=MathLog(A[i]);
     A[i]=MathLog(High[i]);
     printf("%.15f",A[i]);   
   }
   return(0);
} 

 

 

 

However, I'm not sure how many digits the data window is capable of showing.

If it is a question I had about the decimals it supports. Still, I do not show me more than 8 decimal places, and I instuccion the previous post:

int init()
  {
//---- indicators
//   
   SetIndexBuffer(0,A);
   SetIndexStyle(0,DRAW_LINE,STYLE_SOLID);
 IndicatorDigits(Digits+10);
    return(0);
  }

int start()
  {
 int counted_bars=IndicatorCounted();


if (counted_bars>0)
counted_bars--;
int limit= Bars-counted_bars;


for (int i=0;i<limit;i++)
{
//----
  
  
//     A[i]=(High[i]);
//     B[i]=MathLog(A[i]);
     A[i]=MathLog(High[i]);
     printf("%.15f",A[i]);   
   }
   return(0);
} 

 

Take a look at NormalizeDouble - it might be what you are after.