1
vote
1answer
203 views

To get a certain value of NDsolve of the solution [closed]

I need to solve the differential equations for different values. Once it is solved I want to take, for example, x[29] for each initial condition and plot it as a function of this initial conditions. I ...
0
votes
1answer
80 views

Integral for piecewise function inconsistent with the usual way

I have the following piecewise function: ...
0
votes
1answer
159 views

Sum Over Multiple Indices part 2 [duplicate]

Recently I asked this question as I was trying to see how to write a particular Identity. I asked about how to write the following sum: ...
4
votes
2answers
121 views

How to hide arrow tail in VectorPlot3D?

I want to plot arrow head only, because I want to plot a "surface" consist of all arrow head(draw a little ball or point instead of real arrow head,because a 'surface' with real arrow head is ...
1
vote
0answers
92 views

Am I simulating correctly my hidden markov chain?

I want to simulate a hidden markov model, in which $y_t|y_{t-1},x_t=i \sim N(\theta_0y_{t-1}+\theta_i,\sigma^2)$, where $y_t$ is the observations or data, and $x_t$ is the state variable of the ...
0
votes
2answers
84 views

A simple integral operation

Evaluating the following expression results in a non-zero output FullSimplify[Integrate[2 f[x], {x,0,1}] - 2 Integrate[f[x], {x,0,1}]] I think the output should ...
2
votes
2answers
153 views

Generating a permutation of elements in chunks

Is there a way for me to generate a list of permutations in "chunks" such that I needn't store everything on RAM all at once? Consider that (WARNING: DO NOT RUN! --- Will generate a list with 13! = ...
8
votes
2answers
226 views

Add column heads to a dataset

I have a dataset which I group an then calculate the maximum of an item. When done I get the desired result, but have no column heads. Here the example association (subset of my data): ...
1
vote
2answers
84 views

Subroutine execution repetition

I like to write second and third lines repeated operation only once as a separate module with some Name. In each main program line a set of different set boundary conditions data is given,Name invoked ...
15
votes
1answer
303 views

Bug in plotting function using FindMinimum?

Bug introduced in 10.0 and persisting through 10.3 or later While working on an answer to RegionPlot from NDSolve, I came across this strange behavior of ...
1
vote
0answers
67 views

strange behavior when calling external linux command

My platform is Mac OS X Yosemite 10.10.1. When calling several external linux commands as the following: ...
0
votes
2answers
61 views

Getting RandomChoice to work in Manipulate function

I'm a beginner mathematica programmer and I am tryin to create my first demonstration. This code should represent what happens if one changes the size of the reading frame, calculating the nucleotide ...
5
votes
4answers
275 views

HoldForm does not Hold Form for fractions sometimes

I'm facing a strange behavior of HoldForm. I need to display 1/2*3/4 in LaTeX like this : $$ \frac{1}{2} \times \frac{3}{4} $$ ...
0
votes
2answers
96 views

Obtaining the relations of variables using diagonal matrices

I know this is too an elementary question, but I am a pathetic newbie in mathematica and I cannot find any answer by googling. What I want is obtaining some relations of unknown variables using their ...
2
votes
2answers
798 views

Generate nonoverlapping random circles [duplicate]

I want to distribute n circles unformly in an area(e.g. free plannar space). The circles could touch each other but cannot overlap. ...
3
votes
2answers
154 views

WorkingPrecision causes issue in the NIntegrate

I really can't figure out why my code sometimes is not working. My integrals involve two variables (k and kz). The integration ...
5
votes
0answers
230 views

Alternatives to FiniteElement as Spatial Discretization Method for NDSolve

Finite Element Programming: [...] It is possible to skip this section and continue with the discretization stage and make use of the initialized data structures ...
2
votes
0answers
44 views

Error message with RegionPlot after SetOptions

I get an error message with SetOptions[RegionPlot, ImageSize -> Medium]; RegionPlot[u v (1 - v) >= 10, {v, 0, 1}, {u, 0, 100}] that says ...
1
vote
1answer
147 views

Partial differentiation mixes up variables

Consider $$ U \equiv \dot{\theta} - \theta \ ,$$ where as per usual $\dot{\theta} = \frac {d \theta}{dt}$. We then have $$ \frac {\partial U}{\partial \theta} = -1 \quad , \quad \frac {\partial ...
2
votes
1answer
56 views

Double application of NIntegrate produces unexpected error messages [duplicate]

In the course of trying to answer 69601, I encountered unexpected error messages. In highly simplified form, NIntegrate[NIntegrate[z y, {y, 0, 10}], {z, 0, 10}] ...
0
votes
1answer
217 views

NonlinearModelFit - “Encountered a gradient that is effectively zero”, all variables are 1, 1, 1 [duplicate]

I have data of the form {149.45, 0.371093}, {149.362, 0.375976}, {149.277, 0.380858}, ... }, where each element of the list is {x, y}. The plot of this, using ListPlot, gives an approximate Gaussian. ...
0
votes
1answer
178 views

Display 3D function and its gradient in same graphic [duplicate]

Is it possible to display e.g., $z=x^2+y^2$ with Plot3D and in the same box, in the $z=0$ plane, plot its gradient?
14
votes
3answers
615 views

How would I return a random Mathematica command?

I'm doing some metaprogramming. How would I make a Mathematica function that returns a random Mathematica command? Is there a list of command names that I could use ...
0
votes
1answer
116 views

Solve with limit over multiple variables

Very new to Mathematica so apologies for what is probably numpty question. The following returns no solutions. However, there is a solution! If I set a = 1 I get the solution b = 1/2. Can you explain ...
1
vote
1answer
111 views

Why does NMaximize does not follow the constraints that were given to it?

(someone may want to mark it as a duplicate, but I still have to ask! I just can't figure out why!) ...
2
votes
0answers
97 views

ImageResolution Doesn't Work! [duplicate]

The code below is supposed to generate a high resolution plot, but it does not! g = Plot[Sin[x], {x, -1, 1}]; Export["c:/sin.jpg", g, ImageResolution -> 600] ...
2
votes
1answer
327 views

Sinusoidal Wave over a Circle

A sinusoidal wave can be plotted in a two dimensions. Generally and simply : y[x]=Sin[(2pi/lambda)x] As it is being plotted, the horizontal axis (as a straight ...
9
votes
3answers
251 views

Truncating a list once all members of a set have appeared?

Consider if you would the case where we have some list of elements: list0 = {54, 4, 7, 9, 3, 54, 4, 20, 2, 456, 2, 3}; And we have some target list: ...
1
vote
1answer
89 views

Sum of two Piecewise functions give wrong vector

I would like to calculate the normal at a certain point of a parabola. The parabola is defined only on a certain area according to a Piecewise function. Afterwards ...
2
votes
1answer
43 views

Substitution breaking the scope

A novice's problem, perhaps: it seems that /. substitution does weird things to the scope. ...
3
votes
2answers
108 views

How to share numbered variables between kernels

Supose I have two variables v[1] and v[2]. I used: SetSharedVariable[{v[1], v[2]}] Then, ...
1
vote
0answers
188 views

“Home Edition” license for Mathematica: country and upgrades [closed]

I'm interested in buying a "Home Edition" license for Mathematica, but there's the following information which I'd like to know beforehand and which I cannot find online: As I'm about to buy it, the ...
3
votes
2answers
129 views

Substitution in parameters to “Which”

Why in this expression ...
1
vote
0answers
45 views

Which operations preserve digit precision?

Imagine I had to use numbers with a 600 precision digits. Do all mathematical operations, like +,-,...
1
vote
1answer
104 views

Two dimensional high oscillated numerical integral

I have some problem with two dimensional integral. I want to calculate such integral. ...
2
votes
0answers
76 views

How to combine several plots with this special alignment? [duplicate]

How can combine different plots just as shown in the image? Just give codes about one example plot,and tell me how to create plots as the form as gaven. Follows are codes: n = 2; z = 200; [Alpha] = ...
4
votes
0answers
160 views

HEALPix grid on a sphere

Are there any Mathematica tools for using the HEALPix ( Hierarchical Equal Area isoLatitude Pixelation) grid on a sphere? It is commonly used in astronomy, but I have not found any Mathematica ...
5
votes
1answer
171 views

Ruth-Aaron quadruple challenge

This a computational challenge, to find an efficient algorithm to discover a quadruple $(n,n+1,n+2,n+3)$ with the same sum of prime factors as described in the MO question, "Ruth-Aaron triples, etc." ...
1
vote
1answer
97 views

The problem (time) caused by ?NumericQ

In here, I asked a related (similar) question. Using ?NumericQ seems have slowed down the entire calculation. But I now have a more serious problem: ...
2
votes
2answers
144 views

Expressions containing globally undefined symbols inside a function where they are defined

Consider the following code. f[a_,b_]:=x; Clear[a,b]; x=a+b; f[1,2] It returns a+b. However, from a certain viewpoint, one ...
1
vote
1answer
81 views

Nested list element at position specified by a list

I'm trying to avoid constructions like Y[[X[[1]], X[[2]], X[[3]]]]. That is we have a nested list (Y) of depth $n$ and another ...
0
votes
2answers
167 views

Exctrating data information from a file.txt

I really did previous long search in the site and I couldn't find any answer that might help me. So I am asking it. I have the following data set, ...
9
votes
4answers
543 views

How discretize a region placing vertices on a specific non-uniform grid

Given a generic region, for example: Ω = ImplicitRegion[ 2 x^2 + 3 y^2 + 2 x y - 2 <= 0 ∧ x^2 + y^2 > .1, {x, y}]; and a non-uniform grid, for ...
3
votes
1answer
140 views

ConversionRules and style inheritance

Take the LaTeX-Article stylesheet stylesheet = FileNameJoin[{"Article","LaTeX-Article.nb"}]; Compare these outputs ...
7
votes
2answers
241 views

RegionPlot from NDSolve

I am having quite a headache using RegionPlot to see the region of acceptance of certain coupled differential equation. I shall elaborate and try to be as ...
0
votes
0answers
78 views

Exporting graphic to pdf acting funny [duplicate]

I have a plot created in a notebook that I usually would right click on and choose Save as pdf. It worked fine until this morning. Shown below, the first plot is what I used to get. The second plot is ...
3
votes
2answers
192 views

How to cut a thick curve in half lengthwise?

Is there any easy way to cut a thick curve in half lengthwise? Example: suppose I have the cardioid shown in the figure below, is there a way to delete either the inner or the outer portion of the ...
4
votes
2answers
318 views

Solving a discontinuous differential-algebraic equation system for plasticity behaviour

I need to solve a discontinuous equation which is typical in theory of plasticity. For a simple case I get the following equation system (reformulated for numerical implementation): $s(t) = ...
2
votes
1answer
208 views

Can't install Workbench on Surface Pro 3

I've been trying to install Wolfram Workbench 2 for a few days on a Surface Pro 3 i5 256 Mb, Windows 8.1, Mathematica 10.0.1, Java 8, without success, I'm getting a bit desperate. For the Eclipse ...
0
votes
0answers
70 views

How to randomly create disks with randomized radii under given specific cover ratio? [duplicate]

I want to create uniformly distributed disks(dots) in a specific rectangular area. Suppose: the disk radii should be uniformly between $a$ and $b$ ($0<a<b$); there is no interaction between ...

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