Mathematica

NDsolve with a quasi random scource
Hello, I have a quick question regarding the use of a pseudo-random scource inside NDsolve. Suppose you have the following: scource[z_,]:= RandomReal[{-5,5}] Then in NDsolve we have NDsolve[f'[z] + f[z] == scource[z],f,{z,0.5}] My question is as the integrator works to solve this system within NDsolv... 20 Feb 2010 06:55

Convexity and graphical display of feasible set
Hello, I am trying to solve a nonlinear optimization problem with two decision variables with Mathematica. I would like to generate a graphical display of the feasible set defined by a nonlinear constraint of the problem and to analyze the convexity (or not) of the feasible set. Could anybody help me for this? ... 19 Feb 2010 04:21

Convexity and graphical display of feasible set
Hello, I am trying to solve a nonlinear optimization problem with two decision variables. I would like to generate a graphical display of the feasible set defined by a nonlinear constraint of the problem and to analyze the convexity (or not) of the feasible set. Could anybody help me for this? Regards, Pra... 18 Feb 2010 06:07

problem with double integral
Hi there, i got a problem: how can i evaluate the following integral: define: i[Q_] := Integrate[(Exp[-a/(4 x) - 4 x]), {x, \[Infinity], Q}] now i want to compute: NIntegrate[1/i[Q], {Q, 0, 1}] what am i doing wrong? how can i integrate that function? ... 19 Feb 2010 04:22

DDFLink
I am happy to announce that my new product DDFLink is ready for sale now. DDFLink is a link product that links Mathematica to the ddfplus real-time financial data engine ("Digital Data Feed"), the data technology that powers barchart.com. - get live streaming real-time financial market data directly from one o... 17 Feb 2010 20:11

Date & Time format..
Hi I have a list of date and time string such as.. AA = {"Start", "Time", "11/4/2009", "3:24:06.505", "PM"} I want to read "11/4/2009", "3:24:06.505", "PM" as date format.. so I did DateList["11/4/2009 3:24:06.505 PM"] and actually it gives me as {2009, 11, 4, 15, 24, 6.505} But there is also warin... 25 Feb 2010 18:13

Question about Plot[] algorythm.
Hello, I am wondering that sometimes Plot[] takes a huge number of points where a function changes very slowly. And it takes less points where the function changes rapidly! Consider the following: cache = {}; f[x_?NumericQ] := (AppendTo[cache, x]; 5 Csc[x]); pl = Plot[f[x], {x, 0, 2}, PlotRange -> {Full, {0, 14... 18 Feb 2010 06:07

can't get ListVectorPlot3D to work.
********* HELP states: ListVectorPlot3D[{{ {x1,y1,z1},{vx1,vy1,vz1}}, ...}] generates 3D vector plot from vector field values {vxi,vyi,vzi} given at specified points {xi,yi,zi}. But, I get nothing but an empty box when trying this: pts={ {{3., 0, 0}, {-2.15667, 3.39688, 4.02369}}, {{0.843326, 3.39688, 4.023... 17 Feb 2010 07:44

PolarPlot in dB
Hi... I'm trying to plot a radiation pattern using the PolarPlot function, but need to use a dB scale for the magnitude. I would also like to have an angular lines and circles at defined increments. I've searched and couldn't find anything... Anyone know of a way to do this? Thanks Marc ... 17 Feb 2010 00:07

need help determined time to travel a path
I am trying to determine the time to travel a circular path. This path is on a circle. It's fairly easy to understand. But, I can't seem to figure out why this is failing. (* define my parametrizations *) circlex[t_]:=13+13*Sin[t+pi]; circley[t_]:=13+13*Cos[t+pi]; (* the derivatives *) dcirx[t_]:=D[circlex... 17 Feb 2010 00:07