Also we want to make a summ of two numbers. We have two input files - a%i.txt and b%i.txt. And the result of summ will be saved into output.txt.

%i - means that we have a set of files with such names as a1.txt, a2.txt b1.txt, b2.txt and so on. Using %i we may work with dinamycaly created datasets in runtime, where the number of datasets is depended from input data.

So if we have files a1.txt, a2.txt, a3.txt and b1.txt, b2.txt, b3.txt - we will have 3 datasets. For dataset number 1 will be made the summ of values from a1.txt and b1.txt. For dataset 2 - a2.txt and b2.txt and so on.

Also we need a script that will calculate a summ. For example:

 #!/bin/bash
#
#PBS -l nodes=1,walltime=0:25:00
#PBS -e err.out
#PBS -o std.out

input1=#a
input2=#b

#cd to the work dir
path=`dirname $input1`
cd $path

#calculate summ
var=0
num=`cat $input1`
var=$num
num=`cat $input2`
let "var += $num";

#save result 
echo $var > output.txt

Values #a and #b (line numbers 7 and 8) will be replased with real file names a1.txt...b1.txt... in runtime.