# Tagged Questions

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.

226 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: ...
641 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 ...
464 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: ...
240 views

### Correct usage of GeoPosition

My goal is to trace a ray down to the ground. I have done: ...
187 views

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

I noticed that I often turn out to have a list of substitutions in the form ...
180 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 ...
254 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 ...
112 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: ...
2k 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 ...
383 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 ...
792 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 ...
580 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 ...
473 views

### Is it possible to define custom compound assignment operators like ⊕= similar to built-ins +=, *= etc?

I would like to do something like this: ...
828 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 ...
530 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, ...
241 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 ...
482 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 ...
139 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: ...
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 ...
829 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 ...
173 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] <...
265 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 ...
350 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 ...
118 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 ...
142 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: ...
643 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 ...
688 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 ...
575 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 ...
2k 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 ...
403 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 ...
2k 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: ...
114 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 ...
161 views

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123 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 ...
428 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: ...
110 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 ...
115 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 ...
146 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 ...
354 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 ...
283 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: <...
716 views

### Why is EigenValues returning Root expressions? [duplicate]

This is the code I have: ...
101 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 ...
561 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 : ...
2k 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: ...
121 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: ...
608 views

### Splicing a list of arguments into a function with Sequence

Not sure if this has been asked, but I have a fairly simple operation that I don't know the syntax for. Say I have an array with some values, and a function f that accepts an arbitrary number of ...
897 views

### What is the difference between prefix/postfix notations and map?

I am new to Mathematica and just experimenting with the different programming constructs. I have been looking at Map and how to evaluate a function for a list of ...
13k views

### What does # mean in Mathematica?

I asked Mathematica to compute the following Solve[c (1-x)^2-x^(1/4) == 0, x] and it returned this: x = Root[#1^8 c^4 - 8 #1^7 c^4 + 28 #1^6 c^4 - 56 #1^5 c^...
142 views

### When is Evaluate needed within function arguments? [duplicate]

I'm trying to do a simple variable substitution within a ContourPlot, but it's not working. Here's an example: ...
420 views

### Functions that remember their values

Can someone explain what is going on with the following ... func[y_] := func[y] = (Print["Hello world !!!"];) func[1] Hello world !!! ...