143 lines
5.3 KiB
Markdown
143 lines
5.3 KiB
Markdown
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# MathLog
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The function returns a natural logarithm.
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```
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double MathLog(
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double val // value to take the logarithm
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);
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```
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Parameters
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val
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[in] Value logarithm of which is to be found.
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Return Value
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The natural logarithm of val in case of success. If val is negative, the function returns NaN (undetermined value). If val is equal to 0, the function returns INF (infinity).
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Note
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Instead of MathLog() you can use log().
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Example:
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```
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#define GRAPH_WIDTH 750
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#define GRAPH_HEIGHT 350
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#include <Graphics\Graphic.mqh>
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CGraphic ExtGraph;
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//+------------------------------------------------------------------+
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//| Script program start function |
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//+------------------------------------------------------------------+
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void OnStart()
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{
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//--- get 9 values from 0 to 8 with step 1
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vector X(9,VectorArange);
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Print("vector X = \n",X);
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//--- calculate the logarithm for each value of the X vector
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X=MathLog(X);
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Print("MathLog(X) = \n",X);
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//--- transfer the calculated values from the vector to the array
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double y_array[];
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X.Swap(y_array);
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//--- draw a graph of the calculated vector values
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CurvePlot(y_array,clrDodgerBlue);
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//--- wait for pressing the Escape or PgDn keys to delete the graph (take a screenshot) and exit
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while(!IsStopped())
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{
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if(StopKeyPressed())
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break;
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Sleep(16);
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}
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//--- clean up
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ExtGraph.Destroy();
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/*
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result:
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vector X =
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[0,1,2,3,4,5,6,7,8]
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MathLog(X) =
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[-inf,0,0.6931471805599453,1.09861228866811,1.386294361119891,1.6094379124341,1.791759469228055,1.945910149055313,2.079441541679836]
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*/
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}
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//+------------------------------------------------------------------+
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//| Fill a vector with 'value' in 'step' increments |
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//+------------------------------------------------------------------+
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template<typename T>
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void VectorArange(vector<T> &vec,T value=0.0,T step=1.0)
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{
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for(ulong i=0; i<vec.Size(); i++,value+=step)
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vec[i]=value;
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}
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//+------------------------------------------------------------------+
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//| When pressing ESC, return 'true' |
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//| When pressing PgDn, take a graph screenshot and return 'true' |
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//| Otherwise, return 'false' |
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//+------------------------------------------------------------------+
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bool StopKeyPressed()
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{
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//--- if ESC is pressed, return 'true'
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if(TerminalInfoInteger(TERMINAL_KEYSTATE_ESCAPE)!=0)
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return(true);
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//--- if PgDn is pressed and a graph screenshot is successfully taken, return 'true'
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if(TerminalInfoInteger(TERMINAL_KEYSTATE_PAGEDOWN)!=0 && MakeAndSaveScreenshot(MQLInfoString(MQL_PROGRAM_NAME)+"_Screenshot"))
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return(true);
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//--- return 'false'
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return(false);
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}
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//+------------------------------------------------------------------+
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//| Create a graph object and draw a curve |
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//+------------------------------------------------------------------+
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void CurvePlot(double &x_array[], double &y_array[], const color colour)
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{
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ExtGraph.Create(ChartID(), "Graphic", 0, 0, 0, GRAPH_WIDTH, GRAPH_HEIGHT);
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ExtGraph.CurveAdd(x_array, y_array, ColorToARGB(colour), CURVE_LINES);
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ExtGraph.IndentUp(30);
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ExtGraph.CurvePlotAll();
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string text1="Press ESC to delete the graph and stop the script, or";
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string text2="Press PgDn to create a screen, delete the graph and stop the script";
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ExtGraph.TextAdd(54, 9, text1, ColorToARGB(clrBlack));
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ExtGraph.TextAdd(54,21, text2, ColorToARGB(clrBlack));
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ExtGraph.Update();
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}
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//+------------------------------------------------------------------+
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//| Take a screenshot and save the image to a file |
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//+------------------------------------------------------------------+
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bool MakeAndSaveScreenshot(const string file_name)
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{
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string file_names[];
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ResetLastError();
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int selected=FileSelectDialog("Save Picture", NULL, "All files (*.*)|*.*", FSD_WRITE_FILE, file_names, file_name+".png");
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if(selected<1)
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{
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if(selected<0)
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PrintFormat("%s: FileSelectDialog() function returned error %d", __FUNCTION__, GetLastError());
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return false;
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}
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bool res=false;
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if(ChartSetInteger(0,CHART_SHOW,false))
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res=ChartScreenShot(0, file_names[0], GRAPH_WIDTH, GRAPH_HEIGHT);
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ChartSetInteger(0,CHART_SHOW,true);
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return(res);
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}
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```
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Result:
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See also
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[Real types (double, float)](/en/docs/basis/types/double), [Statistics](/en/docs/standardlibrary/mathematics/stat), [Scientific Charts](/en/docs/standardlibrary/graphics), [Client Terminal Properties](/en/docs/constants/environment_state/terminalstatus)
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