## Summation

A summation expression has the form

         sum [<var> = <start> : <end>] <expression>

4#4var5#5 is treated as an integer variable that takes on successive integral values from 4#4start5#5 to 4#4end5#5. For each of these, the current value of 4#4expression5#5 is added to a running total whose final value becomes the value of the summation expression. Examples:

         print sum [i=1:10] i
             55.
         # Equivalent to plot 'data' using 1:($2+$3+$4+$5+$6+...)
         plot 'data' using 1 : (sum [col=2:MAXCOL] column(col))

It is not necessary that 4#4expression5#5 contain the variable 4#4var5#5. Although 4#4start5#5 and 4#4end5#5 can be specified as variables or expressions, their value cannot be changed dynamically as a side-effect of carrying out the summation. If 4#4end5#5 is less than 4#4start5#5 then the value of the summation is zero.