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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6
votes
2answers
1k views

Constructing a Summation with a Variable Number of Inner Sums

I have a question regarding multiple sums. And my second index depends on the first index. Here it is: $$ \sum_{d=1}^{P}e^{-d}\sum_{\substack{1\leq k_{1}\leq Q \\ 1\leq k_{2}\leq Q \\... \\...\\1\...
8
votes
4answers
747 views

Error when using rule as a list index - { i, x[[i]] } /. i -> 5

I can't seem to use a rule to index a vector. x = Range[10]; { i, x[[i]] } /. i -> 5 I get the following error when evaluating the above code, even if the ...
6
votes
3answers
608 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?
2
votes
1answer
108 views

Table of references [duplicate]

I have a list of variables (say a, b, c, d, e) that I want to assign in a single command. {a,b,c,d,e} = {1,2,3,4,5} would ...
1
vote
1answer
381 views

Compile with array operations

When I use the function f with only the Module ...
0
votes
0answers
98 views

My “N” turned red randomly [duplicate]

For some reason my N function showed up in red even though I haven't noticed it in that color before. The color actually makes the code much more readable but I just don't know if I should be alarmed ...
21
votes
2answers
1k 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 ...
10
votes
1answer
878 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 ...
23
votes
0answers
434 views

A documented syntax of FileNames doesn't work?

Documentation discrepancy present through 10.3 According to the documentation for FileNames under Details: However when I attempt to use this syntax I get an ...
10
votes
1answer
732 views

Explain a Mathematica winning one-liner

...
6
votes
1answer
117 views

A question about two ways to use Default

Usually we define a function with default values by the syntax x_:default, but there is another technique to do this by registering a global default value with <...
13
votes
3answers
2k views

Difference between @ and @@

I am confused by the commands @ and @@. From the documentation, I learnt that @@ is the ...
12
votes
2answers
594 views

Why aren't parentheses ( ) an expression in Mathematica?

Why aren't parentheses ( ) an expression in Mathematica? Can I get an expression in a form where parentheses are represented by an expression?
8
votes
1answer
810 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 ...
8
votes
2answers
4k views

How to reverse the direction of the y axes

I have a similar question to this one. Unfortunately, the answers there didn't help me. I would like to plot a simple function with the normal Plot function. ...
12
votes
3answers
292 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] ...
12
votes
5answers
971 views

Postfix Double Slash Notation with Multiple Parameters [duplicate]

Examples A convenient shorthand that I use frequently is the "double slash" notation to string commands together. For example, I can write: ...
9
votes
5answers
6k 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 ...
13
votes
2answers
575 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 ...
8
votes
3answers
595 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 ...
8
votes
1answer
394 views

Treat all variables as local in a module [duplicate]

In most languages, any variable defined inside a function is considered local. ...
7
votes
3answers
336 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 ...
5
votes
2answers
422 views

Can someone explain this code for joining two lists by the first element of each sublist?

Background (which may be skipped, unless context is needed) I've recently begun learning Mathematica (and only up to chapter 3 of Wellin), but wanted to write some code to get a better feel for ...
2
votes
1answer
351 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 ...
5
votes
1answer
246 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
3answers
1k views

Orthonormalization of non-hermitian matrix eigenvectors

When using Orthogonalize[] one can specify which definition of "inner product" is to be used. For example, ...
4
votes
2answers
185 views

Replacing a function in defined expressions

I'm having a little trouble with substituting functions into an expression. A minimal example is as follows: ...
4
votes
1answer
333 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: ...
4
votes
4answers
292 views

Get Axes Range of Plot?

Say I have some plot plot = Plot[Sin[x], {x,0,10}] (*as an example*) Is there a way I can get the x and y axes min/max values from the "plot" variable? If I ...
2
votes
1answer
81 views

Failure in the use of FullSimplify

My question is about an apparent failure of the function "FullSimplify" to simplify an easy algebraic expression. This is the expression that I ask Mathematica to evaluate: ...
2
votes
1answer
697 views

Why is EigenValues returning Root expressions?

This is the code I have: ...
23
votes
2answers
672 views

What is the difference between Composition (@*) and sequential applications (@)?

What is the difference between f@*g@*h@x and f@g@h@x Both evaluate to f[g[h[x]]] ...
18
votes
3answers
5k views

Guidelines on giving readable names to variables [closed]

I know that one cannot use underscore to a variable name, like degree_of_The_First_Polynomial. But for a long variable name, it ...
7
votes
4answers
196 views

How to select only NotebookObjects that are referring to ordinary notebooks? (not palettes etc.)

There is of course function Notebooks[] But, unfortunatelly it hasn't got useful options in this context. My question is how to pick ...
5
votes
2answers
271 views

Overlapping pure functions

Let say I need and option for Plot: RegionFunction -> (-6 < #2 < 6 &) But I also want those ...
7
votes
2answers
542 views
6
votes
1answer
203 views

How can I define a ⊕ operator?

What is wrong with the following code? CirclePlus := SparseArray[Band[{1, 1}] -> {##}] & a_ ⊕ b_ := CirclePlus[a, b] SetDelayed::write: Tag Function in ...
6
votes
1answer
165 views

Problem overloading D[] using UpValues

First I define an entry of UpValues overloading D[] for expressions with head ftest: ...
4
votes
2answers
678 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 ...
4
votes
1answer
294 views

Upon opening my notebook, I must evaluate cell for code to work properly

I am new to Mathematica. Once I evaluate the cell containing the code, my Manipulate works as desired; however, if I open the file and do not evaluate the cell, the Manipulate goes haywire. Can ...
4
votes
2answers
426 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: ...
4
votes
0answers
65 views

String option names for Cells

They seem to be correctly interpreted. I'm asking because of some minor reasons and a major one: NotebookWrite a Cell with WholeCellGroupOpener option I don't know any official confirmation so let ...
4
votes
1answer
99 views

How to define UpValues of NBSpline when the length of argument is unknown?

I mimic the built-in BSplineBasis[] to build a user-defined function NBSpline[], Namely, ...
3
votes
1answer
60 views

How to set similar constraints on multiple variables in Solve

In this equation: var = {x, y, z, m}; Solve[x + 2y + z + m == 14 && And @@ Thread[2 <= var <= 3], var, Integers] {{x->2,y->3,z->3,m->3},{x->3,y->...
1
vote
1answer
65 views

Display a triangle that rotates at certain rate when space bar is held down?

This question is a follow up on: Open a pop up window that runs a calculation in loop until it is closed? How can I open a pop up to show a picture of a triangle that rotates by ...
-5
votes
1answer
467 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 ...
10
votes
4answers
534 views

Extracting equations from Piecewise expressions

Say I have a PDF: PDF[LogNormalDistribution[1.75, 0.65], x] Calculating it, Mathematica gives me an expression that looks like this: I want to extract the ...
8
votes
1answer
177 views

Invalid Symbol Characters

What unicode characters are invalid as a Symbol name? Ideally I'm looking for a complete list. Here is the current list ...
8
votes
1answer
517 views

Setting the DifferenceOrder Option

I've been playing around with Method in NDSolve[...] and can't quite seem to figure out how to force ...
7
votes
2answers
366 views

What's the purpose of the Unique function?

As the title says: What's the purpose of Unique? I understand that it generates some unique symbol, but when and for what is it to be used? Are there applications ...