How can I save multi variable results in a data structure using Pari?

Question

I have a function that loops over its input and produces zero or more results, with each result consisting of three numbers. I want to keep those results in a data structure (e.g., a matrix or a vector of vectors) but I don't know how many entries there will be until the loop terminates. I need to be able to extract a column of the results (e.g.the first variable of each entry) easily.

Answer 1

First off, please look at the PARI/GP reference for vectors/matrices stuff: https://pari.math.u-bordeaux.fr/dochtml/html-stable/Vectors__matrices__linear_algebra_and_sets.html.

You can use the matrix in your loop as follows:

entries = Mat();

for(i = 1, 1000, {
    your_entry = [i, i+1, i+2];
    entries = matconcat([entries; Mat(your_entry)]);
});

print(matsize(entries))
gp> [1000, 3]

print(entries[,1])  \\ Fetch the 1st column

Hope, it helps.