2019-05-09 02:56:14 -0500 received badge ● Student (source) 2017-01-01 12:28:38 -0500 received badge ● Notable Question (source) 2016-01-31 05:43:51 -0500 received badge ● Popular Question (source) 2015-04-01 14:15:10 -0500 received badge ● Famous Question (source) 2015-04-01 14:15:10 -0500 received badge ● Notable Question (source) 2015-04-01 14:15:10 -0500 received badge ● Popular Question (source) 2014-07-27 01:53:51 -0500 commented question !f2py not working I provided further clarification to my question. 2014-07-26 13:03:48 -0500 asked a question !f2py not working Why is the command line F2PY tool not working with my sage installation? The command !f2py on the sage shell returns f2py* -bash: f2py*: command not found  Do I have to be in the right folder for the tool to work? I run sage in a virtual machine under Windows 7. Sage 6.2 Documentation referring to f2py (the section referring to the command line tool is at the very bottom 2014-07-26 06:34:05 -0500 commented answer Summing polynomials Sorry if that wasn't clear. I understood N to be a finite integer. 2014-07-26 04:00:15 -0500 asked a question Summing polynomials I have a ´Univariate Polynomial Ring in t over Symbolic Ring´ sage: cj_t = (-1)**(j-1)/factorial(j-1)*(-j+a)**(j-1/2)*exp(-j)*(t+j)**(-1)  How can I compute the sum over j from 1 to N? sage: sum(cj_t,1,N)  doesn't work. sage: sum([cj_t for j in [1..N]])  (Python syntax) doesn't work either. 2014-07-26 01:41:39 -0500 commented answer Convert symbolic expressions like sqrt(2) or exp(1) to rational numbers I'll maybe post a separate question for the precision issue. Thank you for your answer. 2014-07-25 14:37:55 -0500 commented answer Convert symbolic expressions like sqrt(2) or exp(1) to rational numbers That sounds good. Is there an advantage in the additional step to working over a field of real numbers? What if I wanted to invert a power series with those coefficients, are rational coeffients better than real numbers? 2014-07-25 14:37:05 -0500 answered a question Convert symbolic expressions like sqrt(2) or exp(1) to rational numbers That sounds good. Is there an advantage in the additional step to working over a field of real numbers? What if I wanted to invert a power series with those coefficients, are rational coeffients better than real numbers? 2014-07-25 12:35:04 -0500 asked a question Convert symbolic expressions like sqrt(2) or exp(1) to rational numbers I have coefficents of a rational polynomial f(x) in terms of symbolic expressions like sqrt(2) and exp(1). How can I convert these coefficients to rational number approximations of them, so that I can work in a structure like a polynomial ring? 2014-07-25 03:45:43 -0500 received badge ● Scholar (source) 2014-07-23 13:38:52 -0500 commented answer Series Reversion Thanks a lot for your help. I think I got the hang of it. 2014-07-22 14:48:39 -0500 answered a question Series Reversion My problem now is how to avoid using the Symbolic Ring. I'm trying to do the following: I want to invert an approximation formula for the Gamma-function. I am using Spouge's approximation. It has terms in the numerator and the denominator. Ithink I can compute them separetely per se, but what if I wanted to do a Pade approximation of the function sage: f = (z+13)^(z+1/2)*exp(z) sage: g = f.pade(5,5)  (it's the term ahead of the sum term in Spouge's approimation) How do I get separate polynomials for the numerator and the denominator that are defined in the right algebraic structure? 2014-07-21 14:50:23 -0500 commented question Series Reversion see above for the instructions 2014-07-20 09:43:13 -0500 commented question Series Reversion I added a line with what y(x) looks like. 2014-07-20 09:42:16 -0500 received badge ● Editor (source) 2014-07-20 08:46:18 -0500 commented answer Series Reversion y(x).power_series(SR) gives TypeError: denominator must be a unit' 2014-07-20 05:43:52 -0500 asked a question Series Reversion I have a rational polynomial f(z) = P(z)/Q(z) which I want to revert (I'm trying to find the inverse of f). I'll pick a simple example, the function f(z) = (1/z-1)^4 sage: z = var('z') sage: z = FractionField(PolynomialRing(QQ, 'z')).objgen() sage: f(z) = (1/z-1)^4 sage: g = f(z).taylor(x,2,4); #I expand f in a Taylor series just to make sure it's a series sage: f.expand().reversion() AttributeError: 'sage.symbolic.expression.Expression' object has no attribute 'reversion' sage: g1 = g.power_series(QQ) TypeError: denominator must be a unit sage: g.reversion() AttributeError: 'sage.symbolic.expression.Expression' object has no attribute 'reversion'  A power series P(z) is not a rational function P(z)/Q(z). That's why the TypeError: denominator must be a unit appears. Is it possible that Sage cannot invert rational polynomials? In the Sage help text the computation is passed to pari first, before using Lagrangian inversion. I thought Sage uses FLINT. Why is it not used for computing the inverse of rational polynomials? EDIT (after answer by slelievre): My problem now is how to avoid using the Symbolic Ring. I'm trying to do the following: I want to invert an approximation formula for the Gamma-function. I am using Spouge's approximation. It has terms in the numerator and the denominator. Ithink I can compute them separetely per se, but what if I wanted to do a Pade approximation of the function sage: f = (z+13)^(z+1/2)*exp(z) sage: g = f.pade(5,5) ` (it's the term ahead of the sum term in Spouge's approximation) How do I get separate polynomials for the numerator and the denominator that are defined in the right algebraic structure?