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Adding lists of numbers in Pari/GP

I've got a .txt file, which contains a sequence of numbers as follows:

a_1
+a_2 
+a_3 
+a_4
+a_5
...

Fix some positive integer n. Using Pari/GP, how can I write down the sequence [a_1, a_1 + a_2*n, a_1 + a_2*n + a_3*n, ...] as a Pari/GP vector? I've been told that I shold use concat(-,-), but I don't know how to do utilize the command.

Solution

  • If I create a file C:\temp\example.txt with the contents:

    100
+300
+301
+10101

    then I can use the following:

    gp > a=readvec("C:\\temp\\example.txt")
%1 = [100, 300, 301, 10101]
gp > b=vector(#a,i,a[1]+n*sum(j=2,i,a[j]))
%2 = [100, 300*n + 100, 601*n + 100, 10702*n + 100]

    Here a is simply a vector representation of the file lines, and b is a vector with #a components whose ith entry is a[1] plus n times the sum from j=2 to i of a[j].

    You could also assign a value to n, like n=666, before you declare b.

    Hope this was what you meant.