Ralf Stephan on Sat, 16 Aug 2014 08:04:21 +0200 |
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Re: Vec() and leading zeros of generating function |
Convert into polynomial first: ? s=x^2 + x^4 + O(x^11) %8 = x^2 + x^4 + O(x^11) ? Vec(Pol(s)) %9 = [1, 0, 1, 0, 0] Now just reverse. On Sat, Aug 16, 2014 at 7:43 AM, Kevin Ryde <user42_kevin@yahoo.com.au> wrote: > Vec() can give terms from a polynomial generating function but it > doesn't include leading zeros. Eg. > > Vec(x^2/(1-2*x) + O(x^5)) > => > [1, 2, 4] > > Is there a good way to start from the zero'th term so I would get > > [0, 0, 1, 2, 4] > > I have to confess to only doing this by cut-and-paste programming, so > perhaps there's something completely different I don't know which is > better. :-) My main use has been to compare against expected or desired > values, so > > want = [1, -1, 1, -1] > Vec(1/(1+x) + O(x^length(want))) == want || error("oops") > > I see some Pol(Vecrev()) can turn the values into a poly for the > compare, but poly -> values helps for printing the values too. >