Problem
You're performing calculations that require summations of large amounts of data (for example, for leastsquares curve fitting) and would like to use builtin functions that make such summation computations easy.
Solution
Use Excel's builtin summation functions such as SUM, SUMSQ, SUMPRODUCT, and SUMX2MY2.
Discussion
Excel includes several builtin functions that make performing summations of large (or small) amounts of data very easy. Perhaps the most common sum function is SUM, which simply adds all values contained in a range of cells. For example, =SUM(B2:B24) adds all the values contained in cells B2 to B24. The range of cells does not have to be contiguous either. For example, =SUM(B2:B24,C2:C24) adds all the values contained in each cell range (you separate cell ranges with commas). You can even include explicit values like this =SUM(B2:B24,1). In this case, the values contained in the range plus the specified value, 1, are added.

Table 71 contains a list with short descriptions of several of Excel's convenient summation functions.
Function 
Syntax 
Description 

SUM 
=SUM(n1, n2, n3, ...) 
Returns the sum of all given numbers, which may include cell ranges and explicit numbers. 
SUMPRODUCT 
=SUMPRODUCT(array1, array2, ...) 
Adds the products of corresponding values in given cell ranges (called arrays). The ranges must have the same number of elements. 
SUMSQ 
=SUMSQ(n1, n2, n3, ...) 
Returns the sum of the squares of given numbers, which may include cell ranges and explicit numbers. 
SUMX2MY2 
=SUMX2MY2(array_x, array_y) 
Returns the sum of the difference of squares of values; i.e., (x2  y2). 
SUMX2PY2 
=SUMX2PY2(array_x, array_y) 
Returns the sum of the sum of squares of values; i.e.,(x2 + y2). 
SUMXMY2 
=SUMXMY2(array_x, array_y) 
Returns the sum of squares of differences of values; i.e.,images/U2211.jpg border=0>(x  y)2. 
See Also
Excel's Insert Function tool makes it easy to browse for builtin functions. For more information, see Recipe 1.10.
Excel also contains a family of functions that allow you to perform conditional sums, and other operations, on data. For example, you can sum all the values in a range of databasetype records that meets a specific criterion. These functions are discussed in Chapter 5.
Using Excel
Getting Acquainted with Visual Basic for Applications
Collecting and Cleaning Up Data
Charting
Statistical Analysis
Time Series Analysis
Mathematical Functions
Curve Fitting and Regression
Solving Equations
Numerical Integration and Differentiation
Solving Ordinary Differential Equations
Solving Partial Differential Equations
Performing Optimization Analyses in Excel
Introduction to Financial Calculations
Index