## Summation

A summation expression has the form

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

var is treated as an integer variable that takes on successive integral values from start to end. For each of these, the current value of expression 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 expression contain the variable var. Although start and end can be specified as variables or expressions, their value cannot be changed dynamically as a side-effect of carrying out the summation. If end is less than start then the value of the summation is zero.