# All Questions

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### Calculate area from RegionPlot directly

I have a region plot, and I would like to calculate the area: ...
1k views

### How do I obtain the enclosed area of this particular parametric plot?

I'm trying to find a way to obtain the enclosed area of this particular plot. Can someone show me how? ...
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### How to Optimize Solution? (Project Euler #14)

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

### NonlinearModelFit giving message NonlinearModelFit::nrlnum:

I'm trying to fit my data using NonlinearModelFit, but I keep getting errors that I don't quite understand how to correct ...
31 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 ...
40 views

### Converting integral equations to differential equations [on hold]

I am trying to use Mathematica to convert integrals to differential equations, of any order. An example of an integral equation is given below, in Mathematica code. Could you please advise as to the ...
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### 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 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 ...
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### NSolve not solving [on hold]

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 ...
571 views

### a problem about simplifing conjugate

the situation is as follows ...
56 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 ...
36 views

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

I am using ListPlot: ...
26 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 ...
38 views

### A question about the syntax

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? ...
39 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 ...
88 views

### Unexpected results from GARCH Processes

I'm playing a bit with Time Series and I've been trying to estimate Garch Processes from different time series. Are TimeSeriesModelFit and ...
120 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 ...
120 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 ...
89 views

### contour plot (cartesian) using spherical coordinates postions

Let´s say that I have a data in the following configuration: { Lat, Long,distance, energy}-> lat, long -> galactic coordinates, distance unit - parsecs (3.2 ly) energy unit- ergs. I need to plot ...
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### Appending elements to a list in parallel table

Is there any way to store values in a list that is being computed in parallel? For example, if ParallelTable is computing some ...
390 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: ...
46 views

### 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 ...
267 views

### How to use the Testing Notebook to test a package?

I think an important purpose of the new Testing Notebook in version 10 should be to test user packages (instead to test the builtin functions in the ...
184 views

### Problems finding intersection points between line and generic function

I'm trying to find Intersection points between a line, which is given by 2 points, and a generic function (I want it to be able to handle polynomial functions, circles/ovals, lines and all ...
23 views

### NonlinearModelFit errors and precision [on hold]

unfortunately this question includes a lot of code. Sorry in advance. I use a data set, which I've made available here: ...
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### 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?
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### Approximation of definite integral by parabolas

This question is related to Trapezoid approximation to definite integral. As promised, I am now asking about how to draw approximation of integrals by parabolas. I tried to modify MarcoB's code, and I ...
222 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. ...
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### How to express $f(x,y) = u(x,y) + i\, v(x,y)$ as $f(z)$

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