// Define your functions here
// Your first function
double func1(double x)
{
	double y = sqrt(x);
	return y;
}

// Your second function
double func2(double x)
{
	double y = x^2;
	return y;
}

// Define pointer for function
typedef double (*PFNSUM)(double);

// This is the Sum function - uses function pointer to call appropriate function
// The Sum computed is a simple sum of y values at each x - you can replace with your algorithm as needed
double Sum(PFNSUM pfn, double xmin, double xmax, double xstep)
{
	double sum = 0;
	for(double x = xmin; x <= xmax; x += xstep)
		sum += pfn(x);
	return sum;
}

// This function makes it accessible from LabTalk
// You can go to script window and type:
//    mysum = LTSum(func1, 0, 5, 1)
// and the LT variable mysum will have your sum value
double LTSum(string strFunc, double xmin, double xmax, double xstep)
{
	PFNSUM pfn;
	// Check name passed from LabTalk and assign pointer accordingly
	if( 0 == strFunc.CompareNoCase("func1") )
		pfn = func1;
	else if( 0 == strFunc.CompareNoCase("func2") )
		pfn = func2;
	else
		return NANUM; // if no match on function name, return missing value
	return Sum(pfn, xmin, xmax, xstep); // else call Sum function to compute
}

// This shows how you will call the Sum function from Origin C
void dd()
{
	// Call Sum by directly specifying function name as argument
	double y = Sum(func1, 1, 2, 1);
}