2021-04-10 17:46:09 +0200 received badge ● Famous Question (source) 2020-12-04 18:04:20 +0200 received badge ● Famous Question (source) 2020-11-25 14:00:38 +0200 received badge ● Popular Question (source) 2020-09-11 19:22:38 +0200 received badge ● Notable Question (source) 2020-09-11 19:22:38 +0200 received badge ● Popular Question (source) 2020-07-21 21:06:09 +0200 received badge ● Notable Question (source) 2020-07-21 21:06:09 +0200 received badge ● Popular Question (source) 2019-08-14 18:15:47 +0200 asked a question How to expand the result of derivative()? I ran:  derivative(acosh(x), x)  and the result was:  1/(sqrt(x + 1)*sqrt(x - 1))  I personally would prefer 1/sqrt(x^2-1) as it's an expanded form and I'm wondering how I can get SageMath to show this. I've tried adding .expand() afterwards and that made no difference to the result. 2019-07-24 16:21:35 +0200 commented answer Complex numerical integration: how can it be performed in SageMath? This specific integral isn't symbolically integratable at all; I originally meant to write the bounds as -infinity to infinity, in that case the solution is the Airy $2\pi Ai(z)$ function. Complex integrals that are analytically integratable (e.g. $\int_{0}^{2\pi} e^{ix} dx$) can be analytically (or symbolically) solved in SageMath, but not numerically solved. 2019-07-24 16:21:35 +0200 received badge ● Commentator 2019-07-24 15:52:17 +0200 commented answer Complex numerical integration: how can it be performed in SageMath? Well, it's a roundabout way of solving it, but sure it's satisfactory. Although, if anyone has a more direct way of numerical integration with complex numbers I'll be happy to accept such an answer. 2019-07-24 15:48:24 +0200 commented answer How to solve Sturm-Liouville problems in SageMath? If you look at my question the conditions are: $y(0)=y(\infty)=0$ (granted, I added that like 30 mins before you published this answer, so maybe you missed it). I didn't really expect desolve to work on this, otherwise my DuckDuckGo search probably would have detected a mention of its use for this purpose (SLEs are a different kettle of fish to usual ODEs in terms of how they are solved, so I would have expected a special mention of them, if desolve could solve them). Nonetheless, I gave it a go, here's the code I used and I placed the error in a comment: https://gist.github.com/fusion809/b3e.... 2019-07-24 14:53:06 +0200 asked a question Complex numerical integration: how can it be performed in SageMath? z=1; numerical_integral(exp(i*(x*z+(x^3)/3)), 0, 1, max_points=100) returns the error: --------------------------------------------------------------------------- TypeError Traceback (most recent call last) in () ----> 1 z=Integer(1); numerical_integral(exp(i*(x*z+(x**Integer(3))/Integer(3))), Integer(0), Integer(1), max_points=Integer(100)) /usr/lib/python2.7/site-packages/sage/calculus/integration.pyx in sage.calculus.integration.numerical_integral (build/cythonized/sage/calculus/integration.c:2943)() 279 to_sub = dict(zip(vars[1:], params)) 280 func = func.subs(to_sub) --> 281 func = func._fast_float_(str(vars)) 282 except (AttributeError): 283 pass /usr/lib/python2.7/site-packages/sage/symbolic/expression.pyx in sage.symbolic.expression.Expression._fast_float_ (build/cythonized/sage/symbolic/expression.cpp:62032)() 11928 """ 11929 from sage.symbolic.expression_conversions import fast_float > 11930 return fast_float(self, *vars) 11931 11932 def _fast_callable_(self, etb): /usr/lib/python2.7/site-packages/sage/symbolic/expression_conversions.pyc in fast_float(ex, *vars) 1704 1.4142135623730951 1705 """ -> 1706 return FastFloatConverter(ex, *vars)() 1707 1708 ################# /usr/lib/python2.7/site-packages/sage/symbolic/expression_conversions.pyc in __call__(self, ex) 224 return self.tuple(ex) 225 else: --> 226 return self.composition(ex, operator) 227 228 def get_fake_div(self, ex): /usr/lib/python2.7/site-packages/sage/symbolic/expression_conversions.pyc in composition(self, ex, operator) 1679 """ 1680 f = operator -> 1681 g = [self(_) for _ in ex.operands()] 1682 try: 1683 return f(*g) /usr/lib/python2.7/site-packages/sage/symbolic/expression_conversions.pyc in __call__(self, ex) 216 div = self.get_fake_div(ex) 217 return self.arithmetic(div, div.operator()) --> 218 return self.arithmetic(ex, operator) 219 elif operator in relation_operators: 220 return self.relation(ex, operator) /usr/lib/python2.7/site-packages/sage/symbolic/expression_conversions.pyc in arithmetic(self, ex, operator) 1651 from sage.functions.all import sqrt 1652 return sqrt(self(operands)) -> 1653 fops = map(self, operands) 1654 if operator == add_vararg: 1655 operator = _operator.add /usr/lib/python2.7/site-packages/sage/symbolic/expression_conversions.pyc in __call__(self, ex) 215 if getattr(self, 'use_fake_div', False) and (operator is _operator.mul or operator is mul_vararg): 216 div = self.get_fake_div(ex) --> 217 return self.arithmetic(div, div.operator()) 218 return self.arithmetic(ex, operator) 219 elif operator in relation_operators: /usr/lib/python2.7/site-packages/sage/symbolic/expression_conversions.pyc in arithmetic(self, ex, operator) 1651 from sage.functions.all import sqrt 1652 return sqrt(self(operands)) -> 1653 fops = map(self, operands) 1654 if operator == add_vararg: 1655 operator = _operator.add /usr/lib/python2.7/site-packages/sage/symbolic/expression_conversions.pyc in __call__(self, ex) 206 except TypeError as err: 207 if 'self must be a numeric expression' not in err.args: --> 208 raise err 209 210 operator = ex.operator() TypeError: unable to coerce to a real number  Likewise: z=1; integral(exp(i*(x*z+(x^3/3))), x, 0, +Infinity)  returns: integrate(e^(1/3*I*x^3 + I*x), x, 0, +Infinity)  . If I add a .n() after it, to numerically evaluate it, I get much the same error as I showed earlier. So, how can I do numerical integration of complex integrands in SageMath? I know that simple complex integrands (e.g. exp(i*x)) can be analytically integrated by SageMath, but numerical integration does not seem to be an option. 2019-07-24 12:32:11 +0200 commented answer How to solve Sturm-Liouville problems in SageMath? Incorrect, because it does not take the boundary conditions into account, nor does it take into account that lambda is an eigenvalue, not just any old parameter. The solution only satisfies the boundary conditions when lambda is a zero of the Airy Ai(x) function. 2019-07-24 12:01:37 +0200 commented question How to solve Sturm-Liouville problems in SageMath? Thanks, shall do. 2019-07-24 07:17:12 +0200 asked a question How to solve Sturm-Liouville problems in SageMath? I've conducted DuckDuckGo searches for "Sturm-Liouville sagemath" and received no usable results, and as a result I am here to ask, how can one solve Sturm-Liouville problems with SageMath? I know how to do so numerically with Julia, GNU Octave and Scilab, using matrices, but is there any way to solve at least some of them analytically in SageMath (e.g. $\frac{d^2 y}{dx^2}-xy = \lambda y$ has solutions $y_n=C\cdot \textit{Ai}(x+\lambda_n)$, where $\lambda_n$ are the zeros of the Airy $\textit{Ai}(x)$ function, if $y(0)=y(\infty)=0$)? Failing this, is there a way to numerically solve them in SageMath (without resorting to its interfaces with the languages I just mentioned)? If it helps, here's the code I use in GNU Octave to solve the aforementioned SLE: # Standard values are for transformation x=(y-L)/(y+L), y in 0, inf # *lin are for x=2/L*y-1 (linear transformation) clear all format long e; N=5000; perc=0.266 Nfrag=round(perc*N); n=0:N; # 75 at N=1k; 162 for N=3k; 225 for N=5k; L=226; t=pi+n'*pi/N; x=cos(t); y=L*(cot(t/2)).^2; ysub=y(2:N); ylintrans = L/2*(x+1); # Chebyshev polys of the first kind T = cos(t*n); # Now for arrays that do not include the endpoints xsub = x(2:N); Tsub = T(2:N,:); Usub = diag(1./sqrt(1-xsub.^2))*sin(acos(xsub)*n); dTsub = Usub*diag(n); dT = [-(n.^2).*(-1).^(n); dTsub ; (n).^2]; dTL = diag(2*L./((y+L).^2))*dT; dTlin = 2/L*dT; D1 = dTL/T; D1lin = dTlin/T; D2 = D1^2; D2lin = D1lin^2; H = D2-diag(y); Hlin = D2lin-diag(ylintrans); H = H(2:N,2:N); Hlin = Hlin(2:N,2:N); [Y, Lam] = eig(H); [Ylin, Lamlin] = eig(Hlin); Lam = diag(Lam); Lamlin = diag(Lamlin); [Lam, IX] = sort(Lam, 'ascend'); [Lamlin, IXlin] = sort(Lamlin, 'ascend'); Y = Y(:,IX); Ylin = Ylin(:,IXlin); aizerochk = abs(airy(0,Lam)); aizerochklin = abs(airy(0,Lamlin)); L errrms = sqrt(aizerochk(1:Nfrag)'*aizerochk(1:Nfrag)/(Nfrag+1)) errrmslin = sqrt(aizerochklin(1:Nfrag)'*aizerochklin(1:Nfrag)/(Nfrag+1)) ain=quad("airynorm",0,100); figure(1) plot(ysub(1:3*N/5), Y(1:3*N/5,1)); figure(2) plot(ysub(1:3*N/5), Y(1:3*N/5,2)); figure(3) plot(ysub(1:3*N/5), Y(1:3*N/5,Nfrag));  . It uses a Chebyshev spectral method on the extrema grid, and then analyses the results. 2019-05-03 22:05:03 +0200 received badge ● Nice Question (source) 2019-04-14 18:25:52 +0200 marked best answer How do I plot a 3D Lorenz attractor with x, y and z labels? I have been attempting to perform a 3D wireframe plot of the solution to the Lorenz equations, which is stored in the variables X, Y and Z. This is what I am presently using (unsuccessfully I might add):  # Plot the result from matplotlib import pyplot as plt from mpl_toolkits.mplot3d import axes3d fig = plt.figure() ax = fig.add_subplot(111, projection='3d') plt.figure(1) plt.xlabel('X(t)') plt.ylabel('Y(t)') plt.zlabel('Z(t)') axes3d.plot_wireframe(X,Y,Z) plt.show()  How do I get this plot to work? I'm guessing you'll probably be able to guess that X, Y and Z are ndarrays, produced from this SageMath script: x,y,z=var('x,y,z') # Next we define the parameters sigma=10 rho=28 beta=8/3 # The Lorenz equations lorenz=[sigma*(y-x),x*(rho-z)-y,x*y-beta*z] # Time and initial conditions N=250000 tmax=250 h=tmax/N t=srange(0,tmax+h,h) ics=[0,1,1] sol=desolve_odeint(lorenz,ics,t,[x,y,z],rtol=1e-13,atol=1e-14) X=sol[:,0] Y=sol[:,1] Z=sol[:,2]  2019-02-16 22:39:31 +0200 received badge ● Notable Question (source) 2019-02-16 22:39:31 +0200 received badge ● Popular Question (source) 2018-11-24 07:32:59 +0200 received badge ● Notable Question (source) 2018-11-11 06:29:47 +0200 received badge ● Famous Question (source) 2017-08-18 08:34:54 +0200 marked best answer How to calculate the double factorial in SageMath? I would like to implement the square root of 2 power series: $\sqrt{2} = -\sum \limits_{n=0}^{\infty}{\frac{(-1)^n (2n-3)!!}{2^n \times n!}}$ (which I obtained from the Maclaurin series of $\sqrt{1+x}$ with $x=1$) in SageMath but I cannot seem to find the double factorial function in the SageMath docs. Is there one? I suppose if a double factorial function is not available I could use this method of finding the double factorial that I found on Wolfram MathWorld: $\Gamma(n+\frac{1}{2}) = \frac{(2n-1)!!}{2^n}\sqrt{\pi}$ 2017-08-17 04:34:18 +0200 commented question How to calculate the double factorial in SageMath? Ya I'm well aware convergence is an issue. This method with N (number of terms) = 10,000 is only accurate to 6 decimal places. I know a far more convergent method of estimating $\sqrt{2}$ is Newton's method. Just wanted to give this a try.