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67
votes
3answers
2k views

How to make use of Associations?

I have been curious about it for long. Now that Mathematica 10 arrives, I think it's time to ask the question: How the new Association data structure would be used ...
47
votes
3answers
3k views

Is Mathematica an Implementation of the Wolfram Language?

I am trying to figure out what the announcement of the Wolfram Language means for Mathematica. Is Mathematica an implementation of the Wolfram Language, or is it something else?
37
votes
1answer
806 views

Incompatible Changes since Mathematica Version 7?

There is documentation of the incompatible changes made to Mathematica with each major release: Incompatible Changes since Mathematica Version 1 Unfortunately that documentation simply stopped ...
35
votes
4answers
554 views

What's the difference between Inactive and HoldForm?

In version 10, Mathematica not only added Inactive / Activate but also highlighted this change in the "New in 10" page (in Core ...
34
votes
2answers
812 views

Why is the new PositionIndex horribly slow?

This issue has largely been mitigated in 10.0.1. New timings for the final test below are: ...
28
votes
2answers
800 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 ...
23
votes
2answers
1k views

Is Mathematica comparable to C++ for creating standalone applications?

At my university, I have a yearly essay. I'm allowed to use any technology for implementing it. I've been coding it in C++ with Qt. I thought of about Wolfram Mathematica because I have some ...
21
votes
2answers
458 views

Why is Query so much slower than Part?

Time for another of these(1),(2) as yet another new-in-10 function appears to have poor performance compared to older alternatives. This time: Query appears to be ...
20
votes
3answers
424 views

Real Numbers in the Wolfram Language

Epilog: Much of the discussion in the answers below revolves around the distinction between Real as a data type and real numbers as a domain or class of numbers (irrespective of the form in which ...
20
votes
1answer
264 views

M9 performance regression for Fold?

Bug introduced in 8.0 and persisting through 10.0.2 or later I noticed an over 10x performance drop on Mathematica v9.0.1 (as Oleksandr R. commented, also v8) compared with v7.01 for this code: ...
19
votes
1answer
555 views

Using Transpose with a list as the second argument

I'm having difficulty understanding the Transpose function. I know what the transpose of a matrix is, not a problem, and I see that applying the ...
18
votes
1answer
373 views

Shorter syntax for Fold and FoldList?

I find it tedious to write out the following: a = {1, 2, 3, 4}; Fold[f, First @ a, Rest @ a] f[f[f[1, 2], 3], 4] It ...
17
votes
1answer
258 views

Why some built-in functions are slow

I just wonder why some built-in functions are slower compared to some other ways using more than one built-in functions for doing same job. consider this example: ...
17
votes
1answer
146 views

Help understanding overloading of Atomics within Block

Usually h @@@ {f[1, 2], f[3, 4]} === {h[1, 2], h[3, 4]} but this is not the case when f is ...
16
votes
3answers
329 views

What does None mean in a control specification for Manipulate?

I am now struggling to understand code that contains the following (simplified) Manipulate structure. ...
16
votes
1answer
314 views

Confused about how Partition works

I have a problem about the padding list about Partition command. For instance, ...
15
votes
0answers
131 views

A bug in the overloading of MemberQ and FreeQ for Association?

Bug introduced in 10.0.0 While answering Pattern match for nested Association I came across behavior of MemberQ and FreeQ in ...
14
votes
3answers
352 views

Make mathematica treat $e_i^2$ as numeric

With NumericQ[symbol] = True, I can declare that a symbol is numeric. I want the expressions matching: $$e_{\text{i$\_$}?\text{IntegerQ}}^2$$ to be treated as ...
14
votes
3answers
187 views

How do I understand ListCorrelate(contains $\{k_L,k_R\}$) when it works for 2-dimentional data?

Two months ago, I asked a question here And @nikie give me a solution: The intuitive way to understand ListCorrelate is that the kernel is "moved" to every ...
14
votes
3answers
176 views

What does `: Hold[$IterationLimit]` mean?

In this answer, what does the : Hold[$IterationLimit] part of the following construct do? ...
14
votes
2answers
289 views

Can't get Append to append a record (association) to a dataset

The Documentation Center item, Computation with Structured Datasets, implies that Append has been extended in V10 to work with datasets. But not on my computer. (I ...
12
votes
2answers
308 views

I define a variable as local to a module BUT then the module uses its global value! Why?

I have a question about modules and local variables. Here's my example: h = 5; Module[{a, h}, a[h_]= h^2; a[4]] (*Out[2] = 25*) I expected the module to ...
11
votes
2answers
4k 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 ...
11
votes
2answers
192 views

How to restore function attributes to default

Adding an attribute to a function is easy and clearing attribute is easy also. But I don't know really how to restore the attributes of a function to its defaults. All I do is quit the kernel or close ...
11
votes
2answers
713 views

Scan vs Map vs Apply

I cannot understand the difference between Apply, Scan, and Map. I have tried to play with ...
10
votes
2answers
313 views

When must I use the Return function?

In a comment to my answer to this question, QuantumDot asks, "Where can I find more information on when I must use the 'Return' function?". I found this too deep a question to be answered by leaving a ...
10
votes
1answer
138 views

Why won't SparseArray let me store values with the head List?

When you attempt to define a SparseArray with elements that have the head List it complains: ...
10
votes
0answers
283 views

Create a new infix operator [duplicate]

It is well known that the infix operator @@ is used as a short form of Apply. For example, both ...
9
votes
6answers
366 views

Product of elements of a list

Sum is for functions; Total is for a list. Product is for a function; what is the command ...
9
votes
5answers
342 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
2answers
119 views

DownValue assignment using Apply

Why does assigning a DownValue using Apply, e.g., ...
8
votes
3answers
667 views

Why are functions called first-class objects in Mathematica?

I've heard lots of people say a function is a first-class object in Mathematica. "Everything is an expression, including function." "There is no distinction between functions and data." Having read ...
8
votes
3answers
207 views

Functions that creates symbol in a specific context

I'm trying to make a function f that takes a symbol, a value, and a context, and creates the symbol in the requested context and assigns it the passed value. The ...
7
votes
6answers
426 views

How to build a list of functions

Having said that I'm no expert, I have some problems in generating a list of functions inside a loop. The functions in the list should depend on the elements of a parameters list, that are read in ...
7
votes
3answers
254 views

Implementing key-value associations in Mathematica 9 with inexact numbers for keys

I'm not sure of what type of problem my issue falls into, so I haven't been able to search forums with any success. If this has already been solved then my apologies! Essentially I'm trying to set a ...
7
votes
1answer
299 views

Find a word's linguistic pronunciation

Is there a way to get a word's linguistic pronunciation given the word as a string? I would like a function LingusticPronunciation such that, for example, ...
7
votes
1answer
199 views

Why can't a string be formed by head String?

Since everything is an expression in Mathematica, why must a string object be formed by "abc" but not by a String[abc] ...
7
votes
1answer
241 views

Defining my own invisible operator

There are some invisible operators in Mathematica (\[ImplicitPlus],\[InvisibleTimes],...
6
votes
2answers
281 views

Why are we so sure about Map results?

I do abuse it often but when I have faced this feature first time I was really suprised: i = 0; (i++; # - i) & /@ Range[5] {0, 0, 0, 0, 0} What am I ...
6
votes
2answers
198 views

Why does Mathematica appear to change the head of certain expressions?

I don't know if the question trivial or not (if so I will delete it), but here is what I have: I know that x x (* x^2 *) Looking at the full form gives ...
6
votes
1answer
97 views

Taking the derivative of a function with indexed variables

I have a number of functions that depend on a variable x. I am using a second, integer variable to index these functions, i.e. something like ...
6
votes
1answer
187 views

Treat all variables as local in a module [duplicate]

In most languages, any variable defined inside a function is considered local. ...
6
votes
1answer
114 views

Mystery with ValueQ

Consider the following ClearAll[jd]; ValueQ[jd] We expect False and get it. Now consider ...
5
votes
2answers
232 views

Overlapping pure functions

Let say I need and option for Plot: RegionFunction -> (-6 < #2 < 6 &) But I also want those ...
5
votes
4answers
184 views

Signed power set of a list

Given {a, b, c, ...} with $n$ elements generate a list with $2^n$ elements. For example, if the list were {a, b, c}, then the ...
5
votes
1answer
95 views

Changing the definition of N: unexpected $RecursionLimit::reclim error

I have some objects represented as follows: Object[data, param] data is a list of numbers, ...
5
votes
1answer
142 views

Problem with With [duplicate]

I am puzzled byWith. it does not seem to work. Please see example below (I have also used Evaluate and ...
5
votes
1answer
305 views

Proper use of arbitrary number of variables

So, I'm working on a project where the number of independent variables is not fixed. Consider a problem of $N$ independent variables, $\boldsymbol{r}$. I want to perform different things with them. ...
5
votes
0answers
209 views

Is everything in Mathematica ultimately stored as a rule?

My current understanding about Mathematica is that everything, at the lowest level, ends up as replacement rules. First question: is this true? Second question: does Mathematica "gloss over" these ...