Sums and Products
This constructs the sum
.
| Out[1]= |  |
You can leave out the lower limit if it is equal to 1.
| Out[2]= |  |
This makes
i increase in steps of 2, so that only odd-numbered values are included.
| Out[3]= |  |
Products work just like sums.
| Out[4]= |  |
| Sum[f,{i,imin,imax}] | the sum  |
| Sum[f,{i,imin,imax,di}] | the sum with i increasing in steps of di |
| Sum[f,{i,imin,imax},{j,jmin,jmax}] | the nested sum  |
| Product[f,{i,imin,imax}] | the product  |
Sums and products.
This sum is computed symbolically as a function of
.
| Out[5]= |  |
Mathematica can also give an exact result for this infinite sum.
| Out[6]= |  |
As with integrals, simple sums can lead to complicated results.
| Out[7]= |  |
This sum cannot be evaluated exactly using standard mathematical functions.
| Out[8]= |  |
You can nevertheless find a numerical approximation to the result.
| Out[9]= |  |
Mathematica also has a notation for multiple sums and products.
Sum
represents a sum over
i and
j, which would be written in standard mathematical notation as
. Notice that in
Mathematica notation, as in standard mathematical notation, the range of the
outermost variable is given
first.
This is the multiple sum
. Notice that the outermost sum over
is given first, just as in the mathematical notation.
| Out[10]= |  |
The way the ranges of variables are specified in
Sum and
Product is an example of the rather general
iterator notation that
Mathematica uses. You will see this notation again when we discuss generating tables and lists using
Table (
"Making Tables of Values"), and when we describe
Do loops (
"Repetitive Operations").
| {imax} | iterate  times, without incrementing any variables |
| {i,imax} | i goes from  to  in steps of  |
| {i,imin,imax} | i goes from  to  in steps of  |
| {i,imin,imax,di} | i goes from  to  in steps of di |
| {i,imin,imax},{j,jmin,jmax},... | i goes from  to  , and for each such value, j goes from  to  , etc. |
Mathematica iterator notation.
