2020-03-12 05:13:09 +0100 received badge ● Popular Question (source) 2020-03-12 05:13:09 +0100 received badge ● Notable Question (source) 2019-07-12 06:57:32 +0100 received badge ● Popular Question (source) 2015-03-14 21:56:46 +0100 received badge ● Scholar (source) 2015-03-14 21:56:42 +0100 commented answer Recurrent definiton of a function Great, adding def H11(r1): r1 = ZZ(r1) ....  resolved the problem. Thanks a lot! 2015-03-14 21:47:20 +0100 received badge ● Student (source) 2015-03-14 21:37:35 +0100 commented question Recurrent definiton of a function @vdelecroix, Thanks, I should have stated the problem more explicitly. I've added the setup to the question. 2015-03-14 20:45:32 +0100 asked a question Recurrent definiton of a function Hi, I am trying to compose a code for calculating the numbers H01 defined as a sum of the following recursively defined numbers: H11(r) = \sum_{a + b = r} a*b/r (H11(a) + H12(a)) * H11(b) H12(r) = \sum_{a + b = r} a*b/r (H11(a) + H12(a)) * (H11(b) + H12(b)) H01(r) = H11(r) + H12(r)  I ended up with the following code: memoH11 = {1:0, 2:1/2} def H11(r1): if memoH11.has_key(r1): return memoH11[r1] else: a = 0 for j1 in range(1,r1): a += j1*(r1 - j1)/r1 * (H11(j1) + H12(j1)) * H11(r1-j1) memoH11[r1] = a return a memoH12 = {1:0, 2:0} def H12(r2): if memoH12.has_key(r2): return memoH12[r2] else: b = 0 for j2 in range(1,r2): b += j2*(r2 - j2)/r2 * ( H11(j2) + H12(j2) ) * ( H11(r2 - j2) + H12(r2-j2) ) memoH12[r2] = b return b def H01(r): return H11(r) + H12(r)  And here problems start. If I just type H01(8)  it produces the incorrect value 27/8. But if I type H01(6), H01(8)  it results the correct tuple (7/6, 15/4). So how to fix the code ? Thanks in advance for any help. 2014-11-17 00:36:39 +0100 commented question plotting a plane section in sage @tmonteil Sorry for misleading notation. X, y and z are functions in two variables p and q. 2014-11-14 22:16:41 +0100 received badge ● Editor (source) 2014-11-14 21:55:50 +0100 asked a question plotting a plane section in sage Suppose I have a parametric surface given by three functions in two variables. Moreover, this surface is immersed in a solid torus like sage: p1 = parametric_plot(( a*(R + x)*cos(z), a*(R + y)*sin(z), a*y ),(p,0,2*pi),(q,0,2*pi))  for some a and R. How can one plot a section of the surface by a plane with Sage?