The obvious straightforward method:

Function test()
 
	String list = TraceNameList("", ";", 1)
	String traceName
	Variable index = 0
 
	traceName = StringFromList(0, list)
	if (strlen(traceName) == 0)
		DoAlert 0, "No YW1"
		return -1
	endif
	wave yw1 = TraceNameToWaveRef("", traceName)
	wave xw1 = XWaveRefFromTrace("", traceName)
 
	traceName = StringFromList(1, list)
	if (strlen(traceName) == 0)
		DoAlert 0, "No YW2"
		return -1
	endif
 	wave yw2 = TraceNameToWaveRef("", traceName)
	wave xw2 = XWaveRefFromTrace("", traceName)
 
	index += 1
 
 	// probably need to make this more general...
 	Duplicate/O yw1, MyNewWave
	// Want to do the subtraction  
	MyNewWave=yw2-yw1 
end

By the way, the second igor tag needed to be slash-igor to close the code segment.

John Weeks
WaveMetrics, Inc.
support@wavemetrics.com

For the case of when the x-waves are different, you need to take the maximum and minimum values into consideration. For instance if xw1 goes from 1-40 and xw2 goes from 10-50, you cant subtract the y values which correspond to x values 1-9, or 41-50 (you can only subtract two numbers if they exist). This can be accomplished by only subtracting from max(xw1[0],xw2[0]) to min(xw1[inf],xw2[inf]). That is, largest of the small values to the smallest of the large values (excluding the outside ranges which do not match).

Next, choose one wave as the basis for your for loop (assuming they have different intervals). For example, I am going to choose xw1. For each value of xw1 in this range (10-40 for the above example numbers), you will need to use interp on yw2. If you always have the case where the intervals of xw1 and xw2 are scalar multiples of eachother, you can avoid using interp but always having the result wave have the same interval spacing as the wave with the fewest datapoints (lowest resolution) and just ignoring the extra data points in the other wave.

yw[i] = yw1[i] - interp(xw1[i], xw2, yw2)

I'm vaguely aware of a notation involving the ? symbol that applies a math operation to only a section of a wave, but I'm not sure if that can be used in here place of a for loop (considering interp is required).

Hi
I wanted to show on a panel the name of the wave subtracted : i,e

WaveSubtracated = StringFromList(1, list)- StringFromList(0, list) 

If you want it for display purposes (read-only) you can use a titlebox. Just change the title of the titlebox to be the new wave name. Fundamentally, this isn't very different than using a SetVariable control, where you change the string that is linked to the control.

string NewTitleStr
titlebox box1 title=NewTitleStr

Thanks to Proland...titlebox works great...Thanks to Johnweeks ..you are right....indeed I will not dive so deep...as I am aware of my limited knowledge in Igor..so I stayed with same xw ..and plotted with same xw....indeed Arithmetic Panel is great ...but as I had to work with many sets of graph, I thought wrote something tailor made would be easy to use for me…I checked codes for it…it seems extremely complex … I thought to so something simple....I need little help.

The code beneath (part of my bigger program) does the subtraction and works on Graph with two trace...Mainly what I want to do is to have option in subtraction (arithmetic) so that using setvar0 and setvar1 control I can define MyNewWave…for example say MyNewWave=
2(wave0)- wave1 where setvar1=wave0 and setvar1=wave1 which I say typed in the servar box. Now in present condition it is always hardcoded as wave2-wave1 or wave1-wave2 (if checkbox 1 is checked) .

If tried to declare setvar as string ...and tried to access setvar value as MyNewWave ( say MyNewWave=2(setvar0)-setvar1..where I say handtyped

setvar1=2(wave0) 
setvar2=wave1 

#pragma rtGlobals=1		// Use modern global access method.
 
Menu "Test Subtrac"
      "Test SubtractA/1", Panel10()
End
 
Variable/G
 
Window Panel10() : Panel
PauseUpdate; Silent 1
NewPanel /W=(80,40,358,280)
 
titlebox box1, pos={52,70},size={130,20}, title= "wave1-wave2"
Button button1, pos={52,100},size={130,20}, proc=iSubtractTraceButton,  title="Subtract Traces"
CheckBox Check1,pos={52,130},size={39,14},title="Reverse",value= 0
SetVariable setvar0  pos={52,150},size={130,20}, value= _STR:"wave0"
SetVariable setvar1  pos={52,170},size={130,20}, value= _STR:"wave1"
 
EndMacro
 
Function iSubtractTraceButton(cntl) : ButtonControl
String cntl
Button $cntl
itestsubtract()
End
 
Function itestsubtract()
 
	String list = TraceNameList("", ";", 1)
	String traceName
	Variable index = 0
       NVAR setvar1
       NVAR setvar1
       Variable Conf1
 
       ControlInfo /W=Panel10 Check1
	             Conf1= V_value
 
	traceName = StringFromList(0, list)
	if (strlen(traceName) == 0)
		DoAlert 0, "No YW1"
		return -1
	endif
	wave yw1 = TraceNameToWaveRef("", traceName)
	wave xw1 = XWaveRefFromTrace("", traceName)
 
	traceName = StringFromList(1, list)
	if (strlen(traceName) == 0)
		DoAlert 0, "No YW2"
		return -1
	endif
 	wave yw2 = TraceNameToWaveRef("", traceName)
	wave xw2 = XWaveRefFromTrace("", traceName)
 
	index += 1
 
       Duplicate/O yw1, MyNewWave
 
	string NewTitleStr
 
	 if (Conf1)
     MyNewWave=yw2-yw1
    // MyNewWave=setvar0 - setvar1
     NewTitleStr =StringFromList(1, list) + " - " + StringFromList(0, list)
  //   setvar0  = NewTitleStr
  // setvar1 = StringFromList(1, list)
 
                   else
    MyNewWave=yw1-yw2
    NewTitleStr =StringFromList(0, list) + " - " + StringFromList(1, list)
         endif
 
 titlebox box1, pos={52,70},size={130,20}, title= NewTitleStr
 
	AppendtoGraph MyNewWave vs xw1
	display MyNewWave vs xw1
end

I am really sorry hrodstein..indeed it was my mistake as the same ipf file I had inside the igor procedure folder ..and when saving I did some mistake.......now I corrected (subtractTrace button) and I upload the proper ipf with data file....I still didnt include your addition..I have to include that...thank you so much...now I understand how to use the setvar.

I would recommend a separate setvar for the scalar multiplier. This eliminates the need to parse the string. While splitting the string is possible, you would require the user to be consistent. Splitting "2*wave0" or "wave0*2" are two completely different things.

In regards to setting the value of the setvariable, you do not use ControlInfo.

Instead, use

tracename = stringfromlist(0, list)
Setvariable setVar0 value = _STR:tracename

To update a control, use the same commands you used to make it. Note that you only need to include those which you wish to change (I didn't change the position or size above).