Questions on the basic structure of the Mathematica language (Wolfram language) including atomic data types, syntax etc

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0
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0answers
35 views

when to use `Select` vs `Cases` [duplicate]

Given a list lst and a Boolean function f, are there any interesting differences in the following? ...
5
votes
2answers
246 views

Issue with Set function

Tables often come with column headers. Indexing the columns with the header is a natural thing to do. Although a proper dictionary is the usual solution in such a case, I find it often practical and ...
6
votes
2answers
272 views

What evaluation mechanism is behind Mathematica support for multiple definitions of a function? What is the benefit of this?

I am studying the question What are the most common pitfalls awaiting new users? Up to now, I have fulfilled some of the parts but yet don't understand which this problem is related to? Consider the ...
18
votes
3answers
408 views

What are the requirements for a well behaved indexed variable? Subscript, ToExpression, Downvalue?

On writing this answer I needed to call a function, (NonlinearModelFit) with an unknown number of parameters. We have learned that we should not use ...
0
votes
1answer
63 views

How to put a levelspec in operator form? [closed]

All variable argument functions need Function wrapped around them in operator form, but is there any other way to achieve this: ...
0
votes
1answer
47 views

SortBy second item in each list item [closed]

I have: mydata = {{1, "NEBRASKA", 2.7`}, {2, "NORTH DAKOTA", 3.`}, {3, "UTAH", 3.6`}, {3, "VERMONT", 3.6`}, {5, "HAWAII", 3.7`}} Now, I can do: ...
27
votes
2answers
440 views

Performance regression for Fold?

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: ...
2
votes
0answers
36 views

Unexpected behavior from Return called in a Block [duplicate]

I like to write functions that dispose of failure cases early, before they do the main calculation, but I don't like to write cascading If statements. Here is a toy ...
14
votes
1answer
407 views

Why is an Identity function needed?

Today I came across the function Identity[x] in Mathematica (documentation). The example given in the documentation uses it in ...
0
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1answer
130 views

Help with functions in Mathematica

I'd like to make a function that has many parts. Doing this in something such as Java, which I am familiar with, would be simple. In Mathematica I have these "pieces", which I want to put into a ...
3
votes
4answers
217 views

How can I make a summary of all the commands of Mathematica?

I would like to have a simple way to get summary information about all the many commands built into Mathematica. How could I do this? Is there a site I may refer to?
1
vote
0answers
20 views

How to ValueQ a symbol, constructing the symbol name from strings? [duplicate]

In a function I'm writing, I need to check whether a particular symbol has been assigned a value (any value) in a particular context. This would work: ...
43
votes
4answers
758 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 ...
9
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2answers
234 views

Pattern and Orderless function

I'm a Mathematica beginner. I am exploring the use of patterns and (only for fun) am trying to implement a permutations function. My (dirty) code is: ...
0
votes
1answer
45 views

Could I use Select with condition on any column other than First (Last)? [closed]

I often deal with huge tables of various functions of randomly generated values for my research. Sometimes there's need to only keep rows which satisfy a specific condition. This is easy with ...
2
votes
1answer
63 views
1
vote
0answers
75 views

What's in a Name? [closed]

StringReplacePart["StringReplacePart","At",{14,17}] ... Surely you can't be serious? ... Naming Matters: I think what and how we call things is underestimated ...
27
votes
2answers
599 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 ...
7
votes
2answers
108 views

Cannot Block Plus

It is customary to use the following idiom to partially evaluate something inside a held expression: ...
0
votes
1answer
44 views

The FindRoot output only with numbers [duplicate]

I have this code in Mathematica: FindRoot[{Sin[x - y + 2] - x == 0, Sin[2 x - z] - 8 z == 0, Sin[z + y + z] - 2 x == 0}, {{x, 0}, {y, 0}, {z, 0}}] where it's ...
0
votes
1answer
83 views

solving quadratic and linear congruences with different modulus

We are able to solve the quadratic congruences $C^2 + Q^4 - 2\equiv mod 3072$ and $C - Q^2 - 2046\equiv mod 3072$ by entering ...
0
votes
2answers
51 views

How to make Mathematica to assemble components we already have like a regular input

Suppose we have the following list: {5, 3} I want to add the -> to the end of the first element in the list in Mathematica ...
1
vote
1answer
80 views

How should I enter indexed terms? For example, constants $n_k$ for $k\in\{1,\,\ldots,\,N\}$

How should I enter $\quad \quad \sum^{N}_{k=0}{f(n_k)}$ into Mathematica? More generally, how should I work with the indices? Take the following as an example. I know how the ...
4
votes
1answer
55 views

Boundedness of an expression

First post on this part of the stackexchange network, I was just wondering if Mathematica allows one to quickly see if an expression is always within a certain range given values for the parameters it ...
1
vote
1answer
149 views

A question on using Cases [closed]

I am working on Wagon's FindRoots2D section. Clear[f]; f[x_, y_] := x - y^2 Cos[y]; g[x_, y_] := -y + x Sin[x]; fcnVec[{x_, y_}] := {f[x, y], g[x, y]}; I am ...
0
votes
2answers
38 views

Equality of expressions containing complex numbers [closed]

I am using Mathematica to test the equivalence of symbolic expressions. I run into what appears to be a bug when I test the equivalence of expressions involving an imaginary number taken to a complex ...
3
votes
1answer
44 views

Order of evaluation of Exp and Normal on result from Series

This may be more math related than Mathematica related, but I thought this might be of interest to the group. I'm trying to work with some Taylor Series approximations of functions that are ...
7
votes
1answer
73 views

Is $ModuleNumber working properly on my machine?

In the documentation ref/$ModuleNumber, I read: Every Wolfram System session starts with $ModuleNumber set to 1. Yet, when I quit Mathematica 10.1 (OS X 10.10.4), restart it, open a new notebook ...
14
votes
1answer
272 views

What's wrong with Simplify and FullSimplify?

I have a quite complex list of equations and inequalities I combine to a boundary condition for my cost function. After investigation of two days I found the bug (I really name it a bug!). One of my ...
3
votes
3answers
142 views

How I can count multiplications in an experssion?

Next task to complete: Count *-symbol in such expression as a + s^2*b - c/y + o^3 + n*m*u (in this case count of ...
22
votes
1answer
586 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 ...
2
votes
2answers
121 views

What is wrong with my use of Flatten? [duplicate]

Why does Flatten[f[g[a, f[b]], f[c, d]]] result in f[g[a, f[b]], c, d] I expected the answer to be ...
11
votes
3answers
276 views

How do I make a string literal without having to escape backslashes?

I'd like to say something like: foo = @"\abc\def\ghi" instead of foo = "\\abc\\def\\ghi" How do I do this? This would ...
0
votes
1answer
89 views

Draw a number of rectangles from list of coordinates [closed]

I'm new to Mathematica and this is also my first post here. Now for the question: I try to let Mathematica draw a number of rectangles from lists of coordinates. Unfortunately it only works when I ...
21
votes
1answer
400 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: ...
10
votes
4answers
285 views

How to Thread with custom functions? Thread vs Map?

This function finds n given the nth prime: findPrime[n_] := If[PrimeQ[n], i = 1; While[Prime[i] < n, i = i + 1]; i, False]; This works: ...
2
votes
2answers
98 views

What is the meaning of Range[10] /. {x_ /; PrimeQ[x] -> x^2}? [closed]

I'm currently doing a unit at university that touched briefly on Mathematica, but the final exam will feature multiple choice questions from Mathematica (along with excel and matlab). This leads to ...
5
votes
1answer
209 views

What is the relationship between Thread and MapThread

I hope this is not a silly question, since there are plenty of questions on Thread and MapThread. However, I still cannot quite ...
17
votes
1answer
189 views

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

Bug introduced in 10.0.0 and fixed in 10.1.0. While answering Pattern match for nested Association I came across behavior of MemberQ and ...
12
votes
1answer
172 views

Is there a way to control which special forms Normal converts?

Normal documentation reads: Normal[expr] converts expr to a normal expression, from a variety of special forms. But is there a way to control which special ...
3
votes
3answers
194 views

How to assign symbols to functions

Several functions work with symbols in MMA: Take for example Part: l1=l2=Range[4]; l1[[3]] (*3*) l2[[4]] (*4*) I want to make ...
2
votes
3answers
93 views

Perform For-loop and show output which meets a certain criterion

I am new to Mathematica and I have a For loop like so: For[i = 0, i < 15, i++, PowerMod[i, -1, 15]] Currently it doesn't output anything. The calculation I am ...
2
votes
1answer
86 views

Can I use Switch with an inequality? [closed]

I'd like to have something like: Switch[x, 10, a = 3; b = 7, >10, a = 5; c = 6, _, a = 7; d = 12, b = 1]; I can't seem to get this to work.
26
votes
2answers
2k views

Scan vs. Map vs. Apply

I cannot understand the difference between Apply, Scan, and Map. I have tried to play with ...
3
votes
0answers
248 views

Minimalistic code challenge on Apollonian gaskets

I've been recently fascinated by the beauty, symmetry and mathematical richness of the Apollonian gaskets. So I felt myself challenged to see if it was possible to generate one in Mathematica with ...
0
votes
0answers
46 views

Treating expressions as symbols [duplicate]

I'm trying to do something like this: test = {x, y}; With[{test[[1]] = 3}, x/y] However, the following error is printed: With::lvset: "Local variable ...
0
votes
2answers
45 views

Using Nest on a function that takes a function as one of its arguments [closed]

I have a function, nS[f_, xk_], which takes as arguments a function f and a vector xk. It ...
6
votes
0answers
168 views

Built-in symbols which are more close to the root/core of Wolfram Language

Seeing the vast scope of science covered by the Wolfram Language (WL) and the large amount of built-in symbols (functions), I am curious to know which built-in symbols are more close to the root of ...