Chi2 map - calculate chi2 as a parameter varies

Function chi2generator(fn,ydata,xdata,coefs,whichParam,searchArea, [edata, lhs, rhs])
	FUNCREF chi2fitfuntemplate  fn
	Wave ydata,xdata,coefs      //y data, x data, and coefficient wave
	variable whichParam, searchArea  //which of the parameters to you want to vary, how far from the original value do you want to search (%)
	Wave edata   //wave containing standard deviation for the x,y pair
	variable lhs, rhs    //specify a region of interest in the data using a left hand side and right hand side.

	variable originalvalue = coefs[whichparam]
	variable range = originalValue * searchArea/100
	variable ii

	duplicate/o ydata, :theoretical_data, :chi2_data
	Wave theoretical_data, chi2_data

	make/o/n=200/d chi2_map
	setscale/I x,  originalvalue - range/2, originalvalue + range/2, chi2_map
	
	if(paramisdefault(lhs))
		lhs = 0
	endif
	if(paramisdefault(rhs))
		rhs = numpnts(ydata)
	endif

	for(ii=0 ; ii < numpnts(chi2_map) ; ii+=1)
		coefs[whichparam] = pnt2x(chi2_map, ii)

		theoretical_data = fn(coefs, xdata)
		chi2_data = (ydata-theoretical_data)^2
		
		if(!paramisdefault(edata))
			chi2_data /= edata^2
		endif
		Wavestats/q/R=[lhs, rhs] chi2_data
		
		chi2_map[ii] = V_avg * V_npnts
	endfor

	coefs[whichparam] = originalvalue

	display/K=1 chi2_map

	killwaves/z theoretical_data, chi2_data
End

Function chi2fitfuntemplate(w, x)
Wave w
variable x
End