vectorfunc.lua

function vecadd(a,b)
 res = {};
 for i = 1,#a do
 res[i] = a[i]+b[i];
 end
 return res;
end
function vecsub(a,b)
 res = {};
 for i = 1,#a do
 res[i] = a[i]-b[i];
 end
 return res;
end
function vecmul(a,b)
 assert (type(b)=='number',"vecmul rhs must be a number")
 res = {};
 for i = 1,#a do
 res[i] = a[i]*b;
 end
 return res;
end
function vecdist(a)
 local l = 0;
 for _,v in ipairs(a) do l = l + v*v end;
 return math.sqrt(l);
end

function extrapolate (a,b,distance)
 local diff = vecsub(a,b)
 local dist = vecdist(diff)
 local newdiff = vecmul(diff,distance/dist)
 return vecadd(a,newdiff);
end