Calculations on the values of columns which numbers are given by variables in Gnuplot -

i'm using loop plotting, number of column determined variable. when want calculate difference between 2 columns values doesn't work. want looks approximately in way:

plot [i=2:n-1] fn u 1:($i-$1) w lp 

is not possible in principle use variable column number calculation?

you must use column(i): $1 shortcut column(1).

plot [i=2:n-1] fn u 1:(column(i)-$1) w lp