# All Questions

56 views

### Export NDSolve results

I can see the correct result of my NDSolve when I plot them with large PlotPoints. ...
91 views

### Calculation of 2D FFT for an image

I am trying to obtain 2D FFT of an image. From the 2D FFT, I wish to calculate the amplitude of the FFT averaged over a circle vs the distance in pixels by varying the radius of the pixels which is ...
8 views

### Mathematical formal expression of find “subfunction” in function [closed]

Imagine if I have a function $s(t)$ and $r(t)$. $s(t)$ may contain $r(t)$ one or more times as $s(t)$ is a quasi-period function. What is the correct expression if I want to say the $s(t)$ contains ...
84 views

### How to solve the following fourth order partial differential equation including Laplacian

I wish to solve the following fourth order partial differential equation including Laplacian with the boundary conditions with the initial conditions ...
33 views

### Creating eigenvalues of a matrix [closed]

How do I store eigenvalues of a matrix in a For loop into a two dimensional array and then plot that array?
113 views

### Initializing several values of a function

How do I initialize several values of a function at once? Consider the function f[0] := 1; f[1] := 2; f[2] := 3; f[n_] := f[n] = f[n-1] + f[n-2] + f[n-3]; Is ...
41 views

### Why is the Max function so slow when operating on lists of dates?

Example: dates = DateRange[DateObject[], DatePlus[DateObject[], 15]]; First[AbsoluteTiming[Max[dates]]] (* 21.364247 *) As a workaround, ...
78 views

### Calculate area from RegionPlot directly

I have a region plot, and I would like to calculate the area: ...
91 views

### How to Optimize Solution? (Project Euler #14) [duplicate]

Link to Question: https://projecteuler.net/problem=14 I began by defining the following functions below. ...
49 views

### AppendTo or Part in a ParallelDo?

I have a question regarding how memory is managed in parallel. Specifically, I'd like to know what is the better practice when constructing an array within a ...
148 views

### Defining a function implicitly and calculating its derivatives

I'm interested in using Mathematica's symbolic manipulation to obtain, for a particular function $f$, derivatives of arbitrary order evaluated at zero. Normally I'd use the ...
43 views

### A single point moving at different speeds through different regions on a plot (Manipulate)

I've been working on this for a while with little success. I have a point (that needs to be connected to a Manipulate control in some way), that moves up the plot ...
153 views

### Reject diverging solution of NDSolve

I'm trying to numerically simulate a spring system with complex stiffness. In essence systems of the form $x''(t)+ (a+ ib) x(t)=0$ For this simple example an analytic solution is easy to find. The ...
278 views

### How I can integrate $\int_0^{a} x e^{-\frac{b^2 x^2}{2 c}} J_0(n x) dx$?

How can I get a solution to the integral given below ? $\quad \quad \int_0^{a} x e^{-\frac{b^2 x^2}{2 c}} J_0(n x) dx$ where $a,\,b,\,c$ and $n$ are constants and $J_0$ is a Bessel function of the ...
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### A question about the syntax [closed]

I have $3$ elementary questions to ask and I thank you in advance. Question N°1. What is the right syntax for $$y\equiv0\pmod {2}$$ in the code below? ...
165 views

### Factoring the imaginary unit

Suppose you have this: Collect[2 u + I + 2 + I,I] It gives the same. Is it possible to factor I in elegant way (not ...
77 views

### NonlinearModelFit errors and precision

For this problem, I use a data set, which I've made available here. ...
79 views

### FullSimplify not giving me a physically useful answer for Mott scattering

I am using Mathematica to find the cross-section for Mott scattering over an extended target. I evaluated ...
33 views

### exporting 3D graphics in STL format (for 3D printing) [duplicate]

How do I set the size of the exported item? (Graphics3D has no implied unit, so it is not a-priori clear what size the object will be, and experiment indicates that ...
69 views

### How to use Wolfram language in an external program with low latency?

Im using Wolfram language on Pi B,and I want to compile a '.m' file (like "test.m" that contains Wolfram functions), in an external program like a C/C++ and then Export the output in an image file ...
159 views

### Given a matrix of integer, create a matrix with 1 or 0 according to which numbers are in the first matrix

Not sure the title gives the idea of what I need, so here is a sample: I have ten (w) combinations (subsets) of 20 (n) numbers taken 4 (k) at time. I need a matrix of dimension w x n with 0/1 in each ...
69 views

### Split/unmerge merged cells in notebook file

I have merged cells in a Notebook file. Is there a way to split such a merged cell group back to single cells, in each of them being one command?
41 views

### Import 3D Jpeg file [closed]

How can I import 3D jpeg file to Mathematica ? I would like to import it and save it into a 3D pdf format. This is the images
55 views

### NSolve not solving [closed]

I've been working on a Newton Cooling equation problem for my diff equ class and cannot get NSolve to solve this equation. I've plugged it into Wolfram Alpha and my ...
119 views

### How to solve time dependent coupled differential equations using Floquet method?

I have coupled differential equations D[X[t], t] == M[t] X[t] + R[t] where ...
47 views

### Defining A Function With A Certain Domain

I am trying to plot the numerical range a matrix, which is a set defined like so: $W(A) = \{\langle Ax,x \rangle : x \in \mathbb{C}^n \text{ and } ||x|| = 1\}$ In other words, I am trying to plot ...
63 views

### Large data -list contour plot -list log plot

I've a large data make matrix 100*100 and and other two sets of data represent the x and y axis. Each value in the matrix is a related to one value in x and one value of y. I ask about a way to plot ...
48 views

### Displaying Greek letters with subscripts inside plot [duplicate]

I am using ListPlot: ...
26 views

### How to compare strings insensitive? [closed]

To compare str1 with str2 I would do StringMatchQ[str1, str2] What if I want the ...
676 views

### Finding number of pixels with certain RGB color in an image

I have the following image: To determine the number of black pixels (nBlackPixels) I use: ...
39 views

### How can I move the x-axis label beneath (instead of at the end of) the x-axis?

I borrowed this code from a Wolfram demo. I looked at several answers to the general question of how to move the x-axis label from the end of the x-axis to beneath it (use ...
69 views

### Write list of numbers to a file

I have a list of numbers: e.g. list={1,2,3,4,5} To write the list to a file I use (here each integer number occupies 7 spaces): ...
42 views

### How to express $f(x,y) = u(x,y) + i\, v(x,y)$ as $f(z)$ [closed]

The $f(x,y)$ is actually a series with complex parts. I'd prefer not working this out by hand.
45 views

### Plotting based on all previous equation results [closed]

I have a plot Plot[40500*x^(-0.1), {x, 1, 100}, PlotRange -> {0, 50000}] Now, I am trying to plot the cumulative of these y values. I'll try to explain on an ...
39 views

### How to convert a rational parametric plane curve into implicit form?

This problem is generated from another Green's theorem related question of mine. And here is a forward of the same problem in math.stackexchange. The original equation of the plane curve is not in ...
271 views

### How to Find “n” for n-th Triangular Number

For example, the 7th triangular number is 28. How do I create something that will tell me that 28 is the 7th triangular number? This is what I have created. ...
150 views
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### How can I smooth a 3D surface generated by RegionBoundary?

I have a set of points that belong to the surface of an object. I would like to approximate a surface to which I can compute the distance. of other points. With the nice code of this post, I was able ...
76 views

### How can I convert a fraction to a string that can be used in a file name?

I want add an index to the file names of my exported images, so I'm using ToString. But I have a problem when my index is a fraction, because then the generated ...
54 views

### Mathematica computes wrong eigenvectors? [closed]

I have a matrix M = {{0, 0, 0, 0}, {0, 0, 0, 0}, {0, 0, 0, b}, {0, 0, -b, 0}} that I want to diagonalize. So far, I always used the following and it worked, but ...
54 views

### How to make async functions? [closed]

Considering we have two functions func1 and func2: func1 func2 How can I make ...
14 views

### Selecting elements from list based on list of positions [closed]

I have a list with elements I want to select: list = {1, 34, 98, 4, 5} Now I want to select elements of those list based on a list with positions like: ...
153 views

### How to Write Partition with Infix?

The documentation says that using Infix ~, the following input f[e1,e2,e3,...] can be rewritten as ...
89 views

### Problem with NDSolve: derivative interpreted as square [duplicate]

I am using Mathematica 9, and trying to solve a very easy differential equation with NDSolve. The code I have is s=NDSolve[{y'[x]==y[x],y[0]==1},y,{x,0,1}] but I ...
35 views

### steady state of coupled partial differential equations

I need to solve coupled differential equations(occur regularly in Phase field theory), \begin{eqnarray} \tau \frac{\partial \varphi}{\partial t} &=& W^2\frac{\partial^2 \varphi}{\partial x^2} ...
31 views

### Differentiation and integration [closed]

When I differentiate y, I get: $$y=(x+1)^2$$ $$\frac{dy}{dx}=2x+2$$ When I try to integrate this differential I get: $$y=x^2+2x+C$$ I see that this is incorrect, but I don't understand why. How in ...
100 views

### Help me export high-resolution TIFF figure

I have generated a figure in MMA by ContourPlot3D. How can I export this figure in high-resolution TIFF format(say, 1200 dpi for lines, 300 dpi for halftone and ...
79 views

### Error accumulation in NDSolve?

I'm trying to solve this system of ODEs numerically: $$\vec{Q} = \vec{P} \times \vec{Q}$$ where vectors $\vec{P}, \vec{Q}$ have 3 components: $$\vec{Q} = \left( Q_1, Q_2, Q_3 \right)$$ \vec{P} = ...