Mathematical Analysis with LabTalk


Summary

Many mathematical analysis tools in Origin is accessible from LabTalk script, for example, differentiation, integration, interpolation, averaging multiple curves .etc. Most of these analysis has one or more associated X-Functions, and many commands, objects or arithmetic operators work as an implement to these X-Functions.

When carrying out mathematical analysis, it is sometimes very useful to create a user-interactive dialog to get user input and use the input value(s) for further calculation.

What You Will Learn

This tutorial will show you how to:

  • subtract a line from source data
  • create a user-interactive dialog (getn) to get input from user and make use of the input values
  • use interpolation to compute the Y value for given X
  • normalize a data column
  • calculate average for multiple curves

Steps

  1. Import the data file Waterfall.dat under <Origin EXE folder>\Samples\Graphing folder with the associated import filter into the workbook Waterfall.
  2. // Create a newbook and name it Waterfall (both long and short name)
    newbook name:="Waterfall" option:=lsname;
    // Define the file name and filter name
    string fname$ = system.path.program$ + "Samples\Graphing\Waterfall.dat";
    string filtername$ = "waterfall.oif";  
    // Use the impfile x-function to import the specified file with the import filter
    impfile fname:=fname$ filtername:=filtername$ location:=data orng:=[Waterfall]1!;
  3. Use a loop and the subtract_line X-Function to subtract a simple baseline of end points connection.
  4. //Create new sheet named as SubtractedData
    newsheet name:=SubtractedData;
    //Define the newly created worksheet(current active) as a range variable
    range sdwk = !;
    //Active the "Waterfall" worksheet by its name
    page.active$ = "Waterfall";
    //Define a integral to hold the number of columns in Waterfall sheet
    int nc = wks.nCols;
    //Set the number of columns in SubtractedData sheet to be the same 
    sdwk.nCols = nc;
    //Use the loop and subtract_line x-function to subtract baseline
    //The first and last data points are found and connected linearly
    //This line will be subtracted as baseline from source data
    //Subtracted data will be named by excitation wavelength of source data
    loop(ii, 2, nc)
    {
      range rx = [Waterfall]Waterfall!col(1);
      range ry = [Waterfall]Waterfall!col($(ii));
      subtract_line iy:=[Waterfall]Waterfall!(1,$(ii)) 
      x1:=rx[1] /* Specifies the X value of the first point*/
      y1:=ry[1] /* Specifies the Y value of the first point*/
      x2:=rx[$(wks.maxRows)] /* Specifies the X value of the last point*/
      y2:=ry[$(wks.maxRows)] /* Specifies the Y value of the last point*/
      oy:=[Waterfall]SubtractedData!(1,$(ii));
    //Rename the column long names in SubtractedData sheet
    //Use the User Defined Parameter Wavelength in Waterfall sheet 
     [Waterfall]SubtractedData!col($(ii))[L]$ = [Waterfall]Waterfall!col($(ii))[D1]$ + "nm";
    }


  5. Use a getn dialog to get some user input, let user decide whether to use the peak height at a reference position, or simply the maximum peak height for normalization.
  6. //Create a dialog to get user input of reference peak position X value
    double xx;//give an initial value
    //Create getn dialog
    int n;
    getn
    (Use Specified Reference Peak for Normalization) n:2s
    (Reference Peak Position X Value) xx
    (If not specified, the data will be normalized based on maximum Y value);
  7. Based on the user input from the previous step, loop over all Y columns to do data normalization.
  8. //Create a new worksheet Normalized
    //And set the number of columns to be the same as previous worksheets
    newsheet name:=Normalized cols:=nc outname:=sname1$;
    //Fill in column A with the same data of column A in SubtractedData worksheet
    range r1 = col(1);
    range r2 = [Waterfall]SubtractedData!col(1);
    r1 = r2;
    
    if(n==0)/*If user hasn't chosen "Use Specified Reference Peak for Normalization"*/
      {
        loop(ii, 2, nc)
           {
             //Use the rnormalize x-function to normalize the columns
             rnormalize -r 2 
             irng:=[Waterfall]SubtractedData!col($(ii)) 
             method:=max /*Use "Divided by Maximum" as Normalization method" */
             orng:=%(sname1$)col($(ii));
             wks.col = ii;
             col($(ii))[L]$ = [Waterfall]Waterfall!col($(ii))[D1]$ + "nm";
           }
      }
    if(n==1)/*If user has chosen "Use Specified Reference Peak for Normalization"*/
      {
         loop(ii, 2, nc)
           {
             range rr=[Waterfall]SubtractedData!(1,$(ii));
            //Use interpolation to compute the Y value for given X
            double yy = rr(xx);
            //Use the rnormalize x-function to normalize the columns
            rnormalize -r 2 
            irng:=[Waterfall]SubtractedData!col($(ii)) 
            method:=specify /*Use "Divided by a specified value" as Normalization method" */
            val:=yy /*Use the computed Y value from interpolation as reference value*/
            orng:=%(sname1$)col($(ii));
            wks.col = ii;
            col($(ii))[L]$ = [Waterfall]Waterfall!col($(ii))[D1]$ + "nm";
           }
      }

    Except for the range( ) syntax, several X-Functions can be used for interpolation, e.g. interp1(interpolate Y from X), interp1q(linear interpolation and extrapolation), interp1xy(1D interpolation/extrapolation on a group of XY data).etc

  9. Plot the normalized data as grouped line plots.
  10. //Plot the normalized data as grouped line plots, no legend
    plotxy iy:=(1,2:end) plot:=200 legend:=0;
  11. Calculate the average of multiple curves with the avecurves X-Function.
  12. win -a Waterfall;
    //Create new sheet named as Avecurve
    newsheet name:=Avecurve;
    //Use a loop to calculate the average for every 4 curves
    for(ii=2; ii<nc; ii=ii+4)
    {
    avecurves -r 2 iy:=%(sname1$)(1,$(ii):$(ii+4)) rd:=[Waterfall]Avecurve!col($(ii/2));
    }
  13. Plot the average curve results as another grouped line plot.
  14. //Select the whole worksheet of Avecurve
    worksheet -s 0 0 0 0;
    //Plot the active range as grouped line plot
    plotxy plot:=200 legend:=0;