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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19
votes
5answers
2k views

Clear complains that a subscripted variable is not a symbol or a string?

Here's a small listing where I've used EscqEsc to typeset θ in the notebook: ...
19
votes
1answer
381 views

Why doesn't PatternTest work with Composition?

While playing around with the solutions to this question, I've found some very strange behaviour: ...
50
votes
2answers
1k views

Flatten command: matrix as second argument

One thing I could never wrap my head around is how Flatten works when provided with a matrix as the second argument, and the Mathematica help isn't particularly ...
41
votes
6answers
1k views

Functions vs. patterns

Every time I define a new function, I wonder which construct I should use: true functions obtained by using Function, or rule-based syntax. For example, these are ...
37
votes
2answers
939 views

Head and everything except Head?

I have been working on picking expressions apart using Head and Part and encountered a little mystery. Consider the canonical ...
5
votes
2answers
424 views

Evaluating an If condition to yield True/False

I would like to decide whether an option passed to my custom function has the value Automatic or something else. This is my attempt: ...
20
votes
1answer
464 views

Prefix operator with low precedence

The question is simple, but I will elaborate on the background as well for those interested in the idea: How to define a new operator with specified precedence value? Background Mathematica was ...
6
votes
3answers
982 views

Using D to find a symbolic derivative

I need to do the following: Define a function Take the derivative of this function and have a look at the symoblic representation Substitute in some values With the bonus that I want to use the ...
8
votes
1answer
632 views

What is the difference between Set and SetDelayed?

I have a problem with defining a function and most of time I get confused by Set or = and ...
24
votes
2answers
784 views

Meaning of backtick in floating-point literal

If I compute, say, 1/3//N, Mathematica displays 0.333333 as the result. When I copy that output to use elsewhere, the paste ...
9
votes
2answers
446 views

How can one define an infix operator with an arbitrary unicode character?

You can setup "UsefulFunction[a, b]" to use custom infix notation "a [LeftRightArrow] b" as follows: ...
8
votes
2answers
2k 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 ...
6
votes
1answer
539 views

Coding mistake? [closed]

I have just started using Mathematica with v9.0. I am trying to follow a computation from a book on Fourier series with the function $f(x)=x$ on the interval $-\pi < x < \pi$. Here is the code ...
27
votes
3answers
584 views

Parentheses in pure functions: # & vs. ( # &)

I've been using Mathematica for years, and over time I have developed the habit of using: Select[data, (# == 1 &)] instead of ...
21
votes
4answers
618 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 ...
16
votes
3answers
446 views

How is + as an infix operator associated with Plus?

How is + associated with Plus? Suppose I want to define a head FooBar and have it ...
4
votes
3answers
400 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: ...
2
votes
4answers
338 views

Using the result of Solve in subsequent calculations

I'd like to know how to use the results of Solve in later calculations. Here's what I'm doing now: This is my expression ...
23
votes
1answer
539 views

Convenient string manipulation

With Mathematica I always feel that strings are "second class citizens." Compared to a language such as PERL one must juggle a lot of code to accomplish the same task. The available functionality is ...
22
votes
6answers
414 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 ...
30
votes
4answers
610 views

Usage of \[InvisibleApplication] and other related invisible characters

From the front end, \[InvisibleApplication] can be entered as Esc @ Esc, and is an invisible operator for @!. By an unfortunate ...
11
votes
3answers
401 views

With versus Function

I've seen people compare Block with Module and With as scoping constructs, and try to figure ...
5
votes
2answers
193 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 ...
10
votes
1answer
465 views

Explain a Mathematica winning one-liner

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8
votes
5answers
496 views

can the color in MeshStyle be specified by a ColorFunction, such as “SunsetColors” for example. If so, what is the correct syntax?

This is an example given in Help: Plot3D[Sin[x y], {x, 0, 3}, {y, 0, 3}, MeshStyle -> Gray] Could this be changed to something like ...
20
votes
2answers
630 views

Why there is no name for #1@#2&?

Why does the pure function #1@#2& have no name? Is it due to the way Mathematica works, or is it "just because"? I'm asking because I find inelegant to write ...
10
votes
4answers
380 views

Calling Table with custom iterator

I often find myself in situations where I, for example, need to build a table for some expression, but want to set the number of points rather then the step size, so the code ends up looking like this ...
4
votes
4answers
3k views

Mapping multiple parameters of a function to specific values

I am a little bit confused by the documentation for Apply (@@). I want to define a list of parameters, for instance: ...
10
votes
1answer
167 views

Infix form of PutAppend ( >>> ) does not work with variable

I'm new to Mathematica, so I suspect this question involves either a misunderstanding involving variables or the usage of >>>. On a webMathematica page ...
10
votes
2answers
467 views

How do you programatically load data into symbols?

I am trying to convert a list of string names into symbols, which will then be used to store data. I have 24 files (where the name of each file is a member of the list mentioned above) that I need to ...
5
votes
3answers
227 views

Syntax for prefix mode with multiple arguments using @ shorthand

Is it possible to use the @ symbol with multiple arguments? The Prefix command suggested not. If so, why?
19
votes
2answers
946 views

Code Readability and Object-Oriented Code

The basic problem I have been running into is making readable code, where in other languages I am more familiar with I might have been using class or struct like objects. For example, you can imagine ...
8
votes
2answers
318 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 ...
12
votes
7answers
588 views

Equating matrices (or higher order tensors) element-wise

Say I have two matrices (or, as in my case, higher order tensors) $A,B$, and I want to solve the equation $A=B$. To do so , I need a list of equations that equate entry-wise the elements of $A$ and ...
8
votes
2answers
216 views

Cases[data,Colon[key,_]] vs. Cases[data,key:_] toward XPath, XQuery

Exploring methods to index and search tree-structured key:value pairs via named-entity index (key paths) as opposed to Position-based indexing. Using Rule as ...
11
votes
3answers
170 views

Why can't I use Sequence to perform a Select like task?

Suppose I wanted to write down a list of $p^2$, for $p$ a prime between $1$ and $20$. I would expect Table[If[PrimeQ[k], k^2, Sequence[]], {k, 1, 20}] to work. ...
7
votes
3answers
282 views

how to read in a file in the same directory?

Now I am writing a small package. I have written several files and put them in the same directory. And some files need to read in or include another file in the same directory. But when I simply write ...
7
votes
3answers
298 views

Why can't D[] be used in place here? [duplicate]

Possible Duplicate: General::ivar is not a valid variable when plotting - what actually causes this and how to avoid it? Beginner question: Why can't I use ...
7
votes
5answers
2k views

Notation of partial derivative

I want to write partial derivatives of functions with many arguments. Why is it that when I type f[x,y] ctrl+6 (0,1) it turns out to be bad syntax? The output of ...
6
votes
5answers
277 views

Is it possible to insert arguments into functions when they're used like Function@ or //Function?

Is it possible to insert arguments into functions when they're used like Function@ or //Function? Sometimes I need to do this, but then I have to return to the standard function usage: Function[] ...
2
votes
1answer
135 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
151 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 ...
13
votes
2answers
346 views

How to embed an image into a string?

The documentation for String contains the following statements: Strings can contain any sequence of ordinary and special characters: … Strings preserve ...
6
votes
3answers
335 views

Difference between @ and @@

I am confused by the commands @ and @@. From the documentation, I learnt that @@ is the ...
5
votes
1answer
199 views

Why does the Front End group backslashes into pairs?

What is \\ for? Help finds nothing on it. An odd number of backslashes greater than one are grouped by two and the last one is displayed with a different color. ...
4
votes
1answer
279 views

Path queries for tree-structured data

Can anyone suggest documentation or tutorials for developing path queries and indices for (XML-like) tree-structured data? Suppose data is organized hierarchically in key->value pairs, eg: ...
1
vote
1answer
151 views

Compile with array operations

When I use the function f with only the Module ...
1
vote
1answer
360 views

Why is Euler's number an uppercase “E” and not a lowercase “e”?

Why is Euler's number an uppercase "E" and not a lowercase "e"? Isn't Euler's Number normally expressed with a lowercase "e"?
8
votes
1answer
381 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 ...
11
votes
3answers
238 views

Numbers in alternate bases transcend the evaluator?

It looks to me like a number in a base other than base 10 gets evaluated before the evaluator ever gets a chance to be tweaked. For example, FullForm[16^^abcdef] ...