2020-07-19 19:14:46 -0600 received badge ● Good Question (source) 2017-04-25 08:07:46 -0600 received badge ● Famous Question (source) 2016-08-14 13:05:30 -0600 received badge ● Great Question (source) 2014-10-06 21:51:38 -0600 received badge ● Nice Question (source) 2014-03-28 14:11:53 -0600 received badge ● Notable Question (source) 2013-03-13 15:19:40 -0600 received badge ● Popular Question (source) 2012-11-26 08:41:27 -0600 received badge ● Taxonomist 2012-11-12 07:05:55 -0600 asked a question Rotational 3d How can I rotate a function like f(x)=sqrt(x) (from 0 to3) around the x-axis? I would like to have a 3D picture of the rotational. Thanks. Thomas 2012-07-21 19:07:44 -0600 received badge ● Famous Question (source) 2012-05-04 08:16:51 -0600 received badge ● Good Question (source) 2012-02-06 19:10:07 -0600 received badge ● Famous Question (source) 2012-01-06 08:23:53 -0600 received badge ● Nice Question (source) 2011-11-30 04:40:08 -0600 received badge ● Notable Question (source) 2011-09-22 10:27:56 -0600 received badge ● Notable Question (source) 2011-09-03 11:16:21 -0600 received badge ● Popular Question (source) 2011-08-29 22:07:46 -0600 answered a question Solving a linear equation Or did you intend sage: solve([g1,g2,g3,g4],[a,b,c,d]) instead of... Yes!! Yesterday I sat an hour ...and now I have made a spelling error! Thank you Thomas 2011-08-29 21:58:37 -0600 marked best answer Solving a linear equation Your answer is just one of the ones for this. sage: r1=-62/3675 sage: -10*r1-1/25 473/3675 sage: 25*r1+2/5 -16/735  Maxima returns a solve like this when there is a parameter. In this case, one parameter, r1, which can be any real number. Are you sure your matrix has non-zero determinant? Or did you intend sage: solve([g1,g2,g3,g4],[a,b,c,d])  instead of sage: solve([g1,g2,g3,g3],[a,b,c,d])  Actually, I think this is the real issue - typos trip us all up :( 2011-08-29 09:13:26 -0600 received badge ● Editor (source) 2011-08-29 09:12:56 -0600 asked a question Solving a linear equation Hello, I have a problem with the solution of a linear equation given by sage. sage: a,b,c,d=var('a,b,c,d') sage: v(t)=a*t^3+b*t^2+c*t+d sage: v1(t)=diff(v(t),t) sage: g1=v(0)==0 sage: g2=v(5)==1 sage: g3=v1(5)==0 sage: g4=v(1.5)==0.2 sage: solve([g1,g2,g3,g3],[a,b,c,d]) [[a == r1, b == -10*r1 - 1/25, c == 25*r1 + 2/5, d == 0]]  The right solution is a=-62/3675, b=473/3675, c=-16/735, d=0! What's wrong with my implementation in sage? Thomas By the way: How can I realize the typical pre-formatted "sage:... look" in my postings?? 2011-06-02 02:31:40 -0600 received badge ● Popular Question (source) 2011-03-26 12:01:24 -0600 asked a question How-to: sum Suppose I have defined a function f(x)=x^2  and a list x=[0,1,2,3,4]  Now I can calculate the product x*f(x)  But: If I use the command k=var('k') sum(x[k]*f(x[k]),k,0,4)  I will get the message: TypeError: unable to convert x (=k) to an integer  How can I realize such a summation? 2011-03-26 11:45:09 -0600 commented answer How-to: (Linear ...) regression in Sage Thank you for your answer 2011-03-26 11:44:35 -0600 marked best answer How-to: (Linear ...) regression in Sage It turns out that this has even showed up on Stack Overflow. Luckily, that page refers to the function I had completely forgotten about - find_fit. sage: find_fit? String Form: Namespace: Interactive File: /Applications/MathApps/sage/local/lib/python2.6/site-packages/sage/numerical/optimize.py Definition: find_fit(data, model, initial_guess=None, parameters=None, variables=None, solution_dict=False) Docstring: Finds numerical estimates for the parameters of the function model to give a best fit to data.  So this might work, and looks decent. sage: R = [[1,2],[3.45,4],[6,5],[4,3]] sage: var('a,b') (a, b) sage: model(x) = a*x+b sage: find_fit(R,model) [a == 0.56881365890949054, b == 1.445160655902004] sage: points(R)+plot(model(a=find_fit(R,model).rhs(),b=find_fit(R,model).rhs()),(x,0,10),color='red')  If you are serious about your needs, though, you should probably use some of the tools in Scipy or R (numerous YouTube videos on this, though for reason I can't watch them right now. 2011-03-26 11:44:35 -0600 received badge ● Scholar (source) 2011-03-26 11:44:23 -0600 received badge ● Supporter (source) 2011-03-16 10:18:40 -0600 received badge ● Student (source) 2011-03-15 08:42:53 -0600 asked a question How-to: (Linear ...) regression in Sage Suppose I have the following set of points r = [(1,2),(3.45,4),(6,5),(4,3)]. How do I implement in Sage a (linear) regression with "bord tools"?