# All Questions

59,249 questions
13 views

### Understanding Transpose, dot and at

I found this formula Transpose[{Tv1, Tv2}].Inverse@Transpose@{v1, v2}.{x, y} in some post but lost the link. Now I need to understand why this formula solve my ...
11 views

### How reproduce old SplineFit function?

Prior to version 8, Mathematica included a SplineFit function that could be used, for example, in the form: ...
8 views

### How can empty fields in a csv file be set to Missing when importing as a Dataset?

When importing a csv file with empty fields as a Dataset, the empty fields are set to zero-length strings (""). There is an option, ...
15 views

### How to visualize indifference curve in a 2D plot?

I have two functions f(x,y) and g(x,y). I wish to perform two tasks on a 2-dimensional figure: (1) plot the curve where each point satisfies f(x,y)=g(x,y) (2) mark one side of the curve with red ...
14 views

### running a loop to check for multiple congruences

I have the code for a loop to run. Right now it can check if a number is a square and at the same time check if it is congruent 0 mod 47. My questions is, how can I alter the code to see if it is ...
22 views

### Can NDSolve be used to model gravitational motion due to an ellipsoid?

I'm trying to use Mathematica to get a numerical estimate and plot of the motion of a point mass in the gravitational field of a fixed, non-rotating ellipsoid. Ideally, I'd like to plot the motion ...
15 views

### Impose conditions on PDF distribution

Consider some data data = {{x1,y1},{x2,y2},...} I organize a density distribution using ...
31 views

### Why do I get different symbols (a) with the same FontFace (Cambria Math)?

When I create an equation in MS Office, it uses Cambria Math, and I get the following when I use variable 'a'. When I try to use Mathematica to create graphics for my files, I can try to use ...
73 views

### ContourPlot — How do I color by contour curvature?

I'm plotting the stream lines of fluid flow past a cylinder, and I would like the colors to increase with contour curvature (i.e. increase as the velocity of the flow increases. Here's a MWE that ...
26 views

### Element-wise multiplication of matrices with different dimension

I am interested in efficient element-wise multiplication of matrices with different dimension. Here is my solution: Matrix 1 with dim = {3, 4, 4} ...
37 views

### Simplifying long expressions leads to memory allocation failure

I am currently trying to manipulate a number of expressions into a particular form that will allow me to determine their poles and zeros: ...
38 views

### Random integers [on hold]

I'm wondering if there is any way to generate 10 random integers (between 1 and 10) in a way where once an integer is selected, it does not get selected again. I've tried using RandomInteger and then ...
27 views

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### Multiple collection of terms

As the title suggests, I am interested in how to perform multiple collection of terms. This means that for a given expression a*x*b + c*x^2*d+a*x*k, I want to ...
16 views

### Ordinal subset in the set of classes

I need to do an unusual classification, which I probably will not achieve only with Classify[]. Features are quite simple vectors composed of numbers and nominal ...
42 views

### Simplify differential expressions

One can differentiate a two dimensional vector like this, ClearAll["Global*"] u[x_, y_] := {f[x, y], g[x, y]} Div[u[x, y], {x, y}] with output ...
86 views

### Adjusting bounding box of PlotLegends in TimelinePlot

I'd like to align the elements of the PlotLegend in a single horizontal row beneath the TimelinePlot, as there is plenty of room ...
65 views

Consider ...
32 views

### Plotting dispersion relation [on hold]

Why is the second funtion dos not appear in the graph ? ...
45 views

### Issues solving system of differential equations [on hold]

d = NDSolve [{x''[t] == (x [t] + a[t])/(-2), a''[t] == -x''[t]/2, x[0] == 0, x'[0] == 1, a[0] == 0, a'[0] == 0}, {x, y}, {t, 20}] Keeps returning the error "To ...
57 views

### How do I divide an integral into parts and sum the total?

I have an exercise looking like this: Analyze the integral $4\int_{0}^{1} \sqrt{1-x^2} \, \mathrm{d} x$ numerically by deviding the interval ${]0,1[}$ into three equal parts, then summarize the ...
336 views

### Sort with assumptions

I have a list which looks like this list = {0, Subscript[x,7], -Subscript[x,3]-Subscript[x,9], -Subscript[x,9]}; and all the $x_i$'s are positive semidefinite (i....
52 views

### Identifying total derivatives

I would like to identify which terms in my expression are a total derivative and which ones are not. For expressions in which all terms are a total derivative, one can simply use integrate to find ...
44 views

### How to define multivariable vector funtion? [on hold]

I would like to define a function of variables having two components as $u(x,y) = (f(x,y),g(x,y))$. I defined such a function as u[x_, y_] := {f[x, y], g[x, y]} ...
44 views

### How to show the answer in terms of another variable

if we have A = 1; B = 44 + 1 output :: B = 45 how we can show B like this output :: B = 44 + A
37 views

### Changing speeds of orbiting bodies with Manipulate

The code below is attempting to simulate the orbits of Earth and Mars along with a Hohmann transfer orbit. Since each one of these bodies orbit at different speeds, I need a way to specify each orbit ...
30 views

### How do I Select when the key of an association is a multi-word string

I have imported some survey responses into a Dataset. I now want to select those rows where the response to "participant type" == "Virtual". I discovered that this ...
31 views

### Keyed Hash for HMAC SHA256

I'm trying to use AWS REST API's (because I can't rely on AWSLink). The sample C# code from Amazon uses this a lot: ...
90 views

### Can pattern assumptions be made reliable?

It is possible to use patterns in assumptions such as f[_]>0. This does not seem to be explained in the documentation but is for instance pointed out in Is it ...
33 views

### Replacing with Elements from a List [duplicate]

I have a fairly complicated expression with nested lists and I want to substitute a given string for each integer. Here's a simple example where ind is my integer-valued data structure and names is ...
287 views

### Derivative of an interpolated function

I am trying to take the derivative of an interpolated function. I am given the function values and the derivatives at some irregular points. Here is my minimal working example to reproduce the error: ...
68 views

### Divide a list into two lists with equal sums

I have a list with L elements. I want to find an index within the list, that divides the list to two separate lists so the sum of elements in each of them are equal....
156 views

### Taking the numerator and the denominator

Is there any way to get the Numerator and the Denominator of an expression split in the same way that Mathematica graphically represents it. Say I have an expression: ...
66 views

### System of coupled differential equations

I am trying to solve the following system of equations, but I get as the output the command itself. ...
26 views

### Monitoring PolynomialReduce/Alternatives for other CAS packages

I have a large generic polynomial That looks like $N = \sum_{i_1,i_2\cdots}c_{i_1,i_2,i_3,\cdots} {x_{1}}^{i_1}{x_{2}}^{i_2}\cdots$ This could have anywhere between 3000-9000 terms with a maximum ...
73 views

### Delete duplicates in tuples

I use the following code to create a list of input parameters: ...
43 views

### How do I uninstall an old version of Mathematica?

My SSD is getting full, and while trying to clean it up, I found one of the largest things on here is an installation of Mathematica 10.3. As this is an outdated version, I would like to remove it, ...
60 views

### Identifying points in the frontier of a set

Let me start with an example. Let $$\mathbf{A}=\begin{bmatrix}3&1\\2&3\\1&5\end{bmatrix},$$ and let $Q=\{\mathbf{q}\vert\mathbf{q}\in\Bbb R^3_+ \land \sum_i^n q_i=1\}$ and \$\alpha=(.5,.5,...