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Mar
8
comment Euler's method for system of differential equation
f[x_, y_, t_] := y; why would you pass in x and t to the function f if they are not used in the body of the function? g[x_, y_, t_] :=0.5x+0.5y and here, t is not used in the body of the function, so why is it passed? if you have the problem description you are trying to solve from the source, can you post it? I am having hard time seeing what you are trying to do.
Mar
8
comment The introduction for Context in Wagner's book is out of date?
Try this for more strange result: x = 5; Begin["temp`"]; x = 6; {x, Global`x} which gives {6,6} ?
Mar
8
comment The introduction for Context in Wagner's book is out of date?
may be you found a bug in the book or a bug in Mathematica :)
Mar
4
comment Breaks in plot & blank plots
try Exclusions->None !Mathematica graphics
Mar
4
comment How to obtain differential equations of motion using Lagrangian dynamics?
Here is a demo demonstrations.wolfram.com/… that uses 3 springs and 2 masses. It has a link to detailed Lagrangian derivation of equations of motion which is similar to your problem (the link is below the demo, in the detailed section)
Mar
4
comment How to obtain differential equations of motion using Lagrangian dynamics?
You do not really count the unstretched length of the spring is L in these problems, since one always starts from the relaxed position. The initial stretched length of the spring is already account for. also the PE in spring is $\frac{1}{2} k x^2$ ? And do you really need a package to do this? You asked same question mathematica.stackexchange.com/questions/43256/… you just need to use the text book formula. One line per one equation. (if you use the textbook formula, I think you'll understand more than using blackbox function)
Mar
4
comment How to solve an inequality
I think you need to write R[k + 1] == R[k] - 2^N[k] Y in there and not R[k + 1] = R[k] - 2^N[k] Y i.e. use == and not = ?
Feb
28
comment Why do InputFields not respond in Manipulate utilizing FindGeometricTransform?
do not put manipulate inside module. Put module inside Manipulate. Specially since you have the same symbol based to the outside module and used inside Manipulate. Manipulate should always (at least that is what I would do) be the outermost. This set up : Module[{a},Dynamic[a]] is what causing the problem I think, without even trying it (where a here is your imag). Manipulate is a DynamicModule.
Feb
27
comment Cannot Plot Function
fyi, I get errors !Mathematica graphics
Feb
25
comment Manipulates Behaving Badly--Why is it autoupdating?
Do not have to look at this now, but an advice: do not put Manipulate inside a Module. Put Module inside Manipulate.
Feb
25
comment Image basics in mathematica
Mathematica does not "define" pixel values. Pixel values are defined by the image itself. Whoever creates an image, decides on the type of the image, and hence what format to store the image data in. This is no different than in Matlab. If you do ImageType[image] it will tell you the type of pixels of the image. byte, 16bit, Real, Bit, ..This is similar to Matlab's imfinfo() function.
Feb
25
comment How to calculate the residue of $1/f(z)$ at a numerical approximation to a root of $f(z)$?
what is LMFDB?....from help it says about Residue Laurent expansion of expr. What is the Laurent expansion of 1/DirichletL[19,10,s]? does it have a Laurent expansion?
Feb
23
comment How can I selectively trigger computations in Manipulate?
fyi, your code above does not run, it has errors in it, on V 9.01 , here is screen shot !Mathematica graphics may be if you fix these first it will help.
Feb
22
comment Prevent FullSimplify from converting trigonometric expressions to exponential
Simplify[TrigReduce[s]] gives (Cos[2 B g t] - I Sin[2 B g t]) Sin[u]^2 but this might not generalize without more testing...
Feb
22
comment Prevent FullSimplify from converting trigonometric expressions to exponential
A small example that shows the problem you have?
Feb
22
comment Explicit multiplication * sign in Mathematica
may be Clear[x, y]; expr = x y; FortranForm[expr] gives x*y then you can give this to Maple. ofcourse you have to test this more to make sure it works for your other expressions.
Feb
22
comment Extract coordinates from a polygon
Since you created the polygon, then you must have its coordinates already? it helps to post a complete self contained example that shows the order of the operations, and not bits and pieces since that makes it hard to follow the logic.
Feb
20
comment How to apply Robin boundary condition in Mathematica
I am just guessing really that FEM will be in V 10. Only someone in WRI would know for sure. But if you type ?"NDSolve`FEM`*" you'll see all the hooks there. See mathematica.stackexchange.com/questions/3292/what-is-ndsolvefem (its been there since V8, so one would expect it is ready by now :)
Feb
20
comment How to apply Robin boundary condition in Mathematica
btw, I just looked at your B.C. (before I just saw you mentioned Robin BC in title.) the B.C. you show is not Robin. In Robin, BOTH Dirichlet and Neumann exist on the same region. What you have above is really a mixed B.C. and not Robin. btw, wait a little bit for Version 10, hopefully it will have finite elements support finally and one can expect to solve these problems much easier with FEM new API
Feb
20
comment How to apply Robin boundary condition in Mathematica
THere is a notebook here that has an example ekayasolutions.com/UCDMath/PDEApplications.php (using finite difference).