Mathematica

Hessian Matrix of a Numerical Defined Function
Dear all, I have to calculate the numerical hessian matrix of a numerical defined function. So i use two time ND, but the result seems to me that is not correct. Let take the function as f(x,y), and the hessian matrix at point (1,1) will be: (1) ND[f[x,1],{x,2},1] (2) ND[f[1,y],{y,2},1] and (3) ND[ND... 18 Jan 2010 06:25

Question about Mathematica
Hi. Can someone help me with the following question: I have a table of a table of number pairs: {{{1,2),(3,-1),{2,-4)},{{1,2},{4,-5},{6,-8}},{{2,-1},{-2,-3},{-4,6}}} How may I find the minimum second element in each sub-table? For example, the first sub-table is: {{1,2},{3,-1},{2,-4}} I would like to... 17 Jan 2010 07:15

NMaximize: Method selection impossible
Hi everyone, I have a function to optimize and I'm using Maximize and NMaximize to find the fastest method. Both functions work, but NMaximize doesn't allow method selection. When I select any of four documented methods, I get an error saying that constraints are not valid. The constraints that are cousing the p... 15 Jan 2010 03:54

help with finding solutions
Hi, I'm new to using mathematica so I'm hoping someone can help. I have 3 equations and a lot of parameters. I know some of the solutions to the equations and I wondered if it's possible to use the solutions I know to evaluate the remaining solutions. I have tried to restructure using GroebnerBasis but after 3-4 day... 15 Jan 2010 03:53

sketch a phase portrait for the nonlinear system
Hi,everyone, I am new in Mathematica.When I try to sketch a phase portrait for the nonlinear system, I don't know how to plan the input values for the ODEs to get the right FIGURE. My example is from a book as follows: ode1[x0_,y0_]:=NDSolve[{x=E2=80=99[t]==y[t],y=E2=80=99[t]==x[t](1-(x[t])^2)+y[t],x[0]==x0,y[0]==y0... 15 Jan 2010 03:53

Mac OS X hard disk space used up by virtual memory
Hi, I'm using Mathematica 7 on Mac OS 10.6. I'm finding that when I'm reading in netcdf files and then outputting gifs created from the data, my hard drive space gets rapidly consumed (presumably by virtual memory), to the point where all 20GB of free space is consumed and Mathematica crashes. This happens after only ... 15 Jan 2010 03:53

Converting date strings to DateList format - a need for speed
I have dates in the first column of large flat files (6000+ rows). The flat files have a header row and may have as many as 20 columns of data besides the dates. A sample of a flat file follows dataFile = {{"DATES", "DATA1", "DATA2"}, {"12/31/84", 1, 1}, {"01/01/85", 1, 1.00239}, {"01/02/85", 0.999206, 1.0023... 15 Jan 2010 07:09

New version of Quantum Mathematica Add-On for Dirac bra ket notation quantum algebra and quantum computing
Dear group: We have an important update (new version) of the free Quantum Mathematica add-on for Dirac bra ket Notation, Quantum Algebra and Quantum Computing. We have created a YOUTUBE channel for our Mathematica add-on with screen cast tutorials: http://www.youtube.com/QuantumMathematica Th... 14 Jan 2010 06:50

Differential Eq.
Hi All, Can anybody kindly tell me how I can solve the following differential equation, with (x[0], x'[0]) = (0, 0): x''[t] -x[t] + g[t] = 0, where g[t] = b*v, for x'[t] > v, g[t] = b*(x'[t]-u), for Abs[x'[t]-u] < v, and g[t] = -b*v. Take b = 5, v = 0.2, and u = 0.1. Draw x[t] v... 15 Jan 2010 03:54

Plotting a curve on a flat torus
I want to plot a curve on a flat torus (i.e. the square with identified opposite edges) so i would like mathematica to join the points of the curve in a way that respect the torus topology. Is there a not too difficult way to do this with Mathematica? Or at least is there an easy way to have the points joined only ... 15 Jan 2010 07:09