Questions on correct (or improved) formulation of Mathematica code to achieve particular results. Use this tag (not "symbol") for questions about all those odd @@ /@ # & and ~ characters.

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5
votes
2answers
234 views

Overlapping pure functions

Let say I need and option for Plot: RegionFunction -> (-6 < #2 < 6 &) But I also want those ...
-5
votes
1answer
255 views

Split dataset based on the first column [duplicate]

I have a dataset which I want to split based on the first column. The data looks like this ...
0
votes
0answers
156 views

Assigning numerical values to constants results in complex coefficients in Equations of Motion

I am using Mathematica to get the Equations of Motion (EOM) for a mechanical system (using Lagrangian Mechanics). While I get the EOM in symbolic form, on introducing the following code for assigning ...
1
vote
3answers
151 views

Equation values into list

Suppose I have a function say $f=x^2$. What I would like is a list (or even better, a list with a grid) which resembles {{1,1},{2,4},{3,9}, ...}. Ideally one should ...
28
votes
2answers
805 views

Is there a name for #1@#2&?

Why does the pure function # @ #2 & have no name? I'm asking because sometimes I find inelegant to write expressions like ...
4
votes
1answer
142 views

DeleteCases vs. DeleteDuplicates for removing points within a critical Euclidean distance

I'm attempting to remove all points in an array which are within a Euclidean distance "ThresDist" of one-another. Using the command: ...
26
votes
6answers
529 views

Constructing symbol definitions for With

I would like to be able to define two arrays, one containing symbol names and one containing the values of those symbols, for use in constructs such as With. For ...
2
votes
1answer
251 views

How to get 'exact' expression for result

I have a result from Mathematica for which want to have the exact expression, i.e. all of the arguments of type # replaced. It is given by: ...
1
vote
1answer
168 views

Correct usage of GeoPosition

My goal is to trace a ray down to the ground. I have done: ...
3
votes
1answer
173 views

Shortening the syntax {var1, var2} /. # & /@ list

I noticed that I often turn out to have a list of substitutions in the form ...
2
votes
2answers
151 views

Extracting counts of contiguous zeros and ones from a binary array

I'm a novice with Mathematica, but you guys have been very helpful to me in the past. I have a binary array [100, J repetitions] consisting of zeroes and ones. I'd like to extract a histogram of the ...
1
vote
1answer
200 views

Bincounting a list

I'm a Mathematica novice here. I'm trying to execute the following code to add random 1's into a zero matrix, repeat this many times, and then bin/histogram the number of nearest neighbor 1s. Can ...
3
votes
1answer
101 views

Export file with semicolon at the end of line

Is there a rule that tells Mathematica to set a semicolon at the end of each line (except of the last one)? My MWE is: ...
4
votes
1answer
838 views

What do the hashtags represent in the result of Solve, and how should I use them? [duplicate]

There is a function that I'm trying to get the inverse of. My function is a simple polynomial: Tn[T_] := 4/9 T^3/Tc^2 + 5/9 T Now I tried to find ...
5
votes
1answer
242 views

How to convert an image to a compressed string representation equivalent to one copied to clipboard by `CopyToClipboard[image]`?

In my recent question I asked How to embed an image into a string? The suggested solution was ...
10
votes
2answers
504 views

How to create custom Graphics primitive?

How to create custom Graphics primitive? It should have the following properties, resembling properties of built-in geometric figures, like ...
13
votes
2answers
475 views

How to embed an image into a string?

Note: The bug described in the post is in Mathematica 9, and has been fixed in 10.0. The documentation for String contains the following statements: Strings ...
5
votes
1answer
396 views

What does ` symbol in ClearAll[“Global`*”] mean?

I have found an example for clearing all symbol definition by: ClearAll["Global`*"] But what does the symbol ` mean? It isn't the apostrophe ', yet it is not ...
2
votes
0answers
294 views

NonLinearModelFit with Two Dimensional List of Weights

I'm currently trying to fit Planck's law (B[λ, T]) to measurements, thereby determining Planck's constant. I have a list of triplets containing wavelength, ...
0
votes
1answer
176 views

Pattern match with Table for matrix dimension check

In Mathematica, often an expression involving matrices will encounter dimension mismatch errors, like we are multiplying a 3x2 matrix to a 3x4 matrix. Below we define a new symbol Dim, which can be ...
13
votes
2answers
360 views

What kind of hypergeometric function is it?

I found a formula for an integral of a product of three Bessel functions at The Wolfram Functions Site: I cannot understand what kind of hypergeometric function it is. The Mathematica code given ...
3
votes
1answer
131 views

Filtering the elements of an array to split them into two categories

So, I am new to Mathematica, and I am trying to write something that involves taking values from one array and separating them into two different arrays. My code for doing this is: ...
31
votes
5answers
1k views

Why is there no PositionFunction in Mathematica?

Too often I have seen the programs of inexperienced users greatly slowed by using Position in an iterative fashion, when far faster would have been to compute a ...
0
votes
1answer
505 views

What is wrong with this Cobweb plot [closed]

Something is wrong with my cobweb plot code but I couldn't figure out where do the mistakes come from. So basically we have the iterative map $x_n == x_{n-1}^{2} - 3 \mu$. I would like to draw a ...
8
votes
1answer
156 views

Different behaviours of Default Argument

I don't really understand the behaviour of Default Argument. If I execute this command in Mathematica: In: {f[a], f[a + b]} /. f[x_ + y_.] -> p[x, y] ...
3
votes
1answer
220 views

Using single replacement rule to convert algebraic expression

I have been trying this problems for hours and cannot find any helpful clues. How can I convert $Sinh[3\theta]+Sinh[\theta]$ to a rational function of x given $2Sinh[\theta] = x-x^{-1}$ by using only ...
1
vote
1answer
230 views

Solve this equation symbolically

I am trying to solve the equation for the quantity r = y/x symbolically: 3/y^4 == 3/x^4 + a/(x + 2 y)^4 with the requirement that we need to perform the ...
3
votes
1answer
105 views

Dt acting on symbolic notational forms

This one must be simple, but I can't figure out a decent solution. Suppose, I have a symbol with a notational form applied to it, say OverHat[A]. Now, if I didn't ...
0
votes
1answer
126 views

How to tell Mathematica to make assumptions? [duplicate]

Say I want to integrate 1/(x^2+a^2) and I want Mathematica to know that $a>0$. What would be the command? Something like: ...
1
vote
2answers
499 views

Translating a “Point-to-Triangle” distance script from MATLAB to Mathematica

Update - Thanks everyone for your responses! After fixing a problem with vector normalization, the code below now works. I'm a new user, and I was attempting to port some Mathematica code from ...
3
votes
2answers
392 views

Write a function that returns the logarithmic derivative

How can we write a function that if we input an expression f, it returns the log derivative $\frac{1}{f} \frac{df}{dx}$. We have to use a conditional or pattern test so that the function accepts any ...
0
votes
1answer
361 views

Mathematica command for type checking?

I have a program where users can enter mathematica commands that can evaluate to any of the standard numeric types (complex, real, int, etc.), or to boolean values. Moreover the users can enter ...
0
votes
2answers
870 views

Why function cannot be defined inside For loop? [closed]

I have a following code (which is simplified version of what I am doing): For[i = 1, i <= 5, i++, f[x_] := Sin[x]^2 Print[{i, f[i]}] ] And the question ...
2
votes
0answers
302 views

Conditional statements in intial conditions?

This is potentially a daft question, but I thought I'd ask it; I have some material free to diffuse in a boundary between rn and ro; I've been able to get it working nicely for neumann type boundary ...
1
vote
2answers
1k views

How does one specify Neumann conditions for NDSolve?

I have a series of functions defined in my notebook, and then want to use this to solve a diffusion-reaction type equation. At the moment, something like this works: ...
6
votes
0answers
109 views

Design considerations behind `O` (a.k.a. BigOh, a.k.a. Landau Order)

This works without any warnings: O[Log[x]]. This raises a warning: O[x^2]. I have a few questions around this: Why is it a ...
0
votes
2answers
89 views

Getting value of clock [duplicate]

I have the following code: a = Dynamic[Floor[Clock[2]]] (*So this basically alternates between 0 and 1*) If[a==1, Print["true"]] But this doesn't work, it ...
4
votes
2answers
371 views

List reversion inspired by Python

In python, if you wish to reverse a list, here is the trick: range(10)[::-1] => [9, 8, 7, 6, 5, 4, 3, 2, 1, 0] Note: ...
1
vote
1answer
94 views

How to programmatically comment out multiple source files?

How to programmatically comment out the entire content of multiple .m source files assuming they start with correct Mathematica syntax? I need it to be robust so ...
4
votes
0answers
88 views

Is there a way to check whether two notebooks share the same variables?

When I code in Mathematica, I often re-use code from old notebooks which fulfilled a specific purpose; for example, one testing for soft matches in strings, or one that identifies outliers on a graph ...
2
votes
2answers
134 views

How to make Mathematica returns the exact expression I typed

I'm using Mathematica to compare some constants. Before playing around with those constants, I would like to check that I didn't make any mistake in typing them. So my question is the following: "What ...
1
vote
1answer
222 views

Syntax for integrating over limits specified by a Table

I wish to use NIntegrate to compute multidimensional integrals. However, I don't want to manually input the limits for the dimensions. I want to store the ...
2
votes
1answer
206 views

Transfer of symbols between contexts

As many others (I guess) I'm struggling with the handling of contexts within Mathematica. I'm working on a new package definition with the usual syntaxt specified by the Mathematica documentation: ...
0
votes
1answer
398 views

Why is EigenValues returning Root expressions?

This is the code I have: ...
0
votes
1answer
93 views

Why does Eigenvalues[matrix I defined] not work? [duplicate]

This is the code I have in my mathematica notebook. I want to find the eigenvalues of the matrix I created called Hmatrix as defined below. However when I type Eigenvalues[Hmatrix] I get the Hmatrix ...
3
votes
2answers
341 views

Why does the first derivative of a piecewise continuous function have discontinuities?

I have this piecewise continuous function which is also continuously differentiable over time : ...
6
votes
3answers
919 views

Keep function range as a variable

Plot[2*x^2 - x + 2, {x, -1, 1}] plots a function of x from -1 to 1. As far as I can see, I cannot "save" this range in a variable: ...
4
votes
0answers
113 views

Proper treatment of roots and powers in Series?

I have the following problem in Mathematica 9 on Linux. I let Mathematica compute the Series expansion: ...