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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57
votes
7answers
3k 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 ...
6
votes
1answer
102 views
3
votes
1answer
87 views

Why minimization does not work with symbolic array as arguments

If I try to minimize with constraints a function of several variables, with Gamma regularized function involved in the constraints it seems to works, as shown below (this is just a dummy example ...
6
votes
0answers
75 views

Negative accuracy numerics ( 0``-128 notation )

What does it mean to have a negative accuracy number? I understand 0``128 to mean "the number zero to 128 decimal points". Mathematica corroborates this: ...
-1
votes
1answer
95 views

How to make sure input is an ODE

I'm having trouble wrapping my head around why this isn't an ordinary differential equation. ...
0
votes
1answer
254 views

How To Use D[ ] to Define a System of PDEs

We have two variables $u_{1}$ and $u_{2}$ which are functions of $x,t$. That is, $u_{1}=u_{1}(x,t)$ and $u_{2}=u_{2}(x,t)$. Consider the the system of partial differential equations $$\frac{\partial ...
3
votes
2answers
226 views

Integrate using \[Esc] int \[Esc]

I like writing integrals symbolically instead of using Integrate[]. I suddenly seem to not be able to do this and am confused. I type \[Esc] int \[Esc] then ...
1
vote
1answer
127 views

Partial derivative of defined function with vector input

Background: Have written a formula for the refractive index for a glass slab (n) that depends on the variables t,a and d. Now I want to calculate for example some sort of error and I'll be needing to ...
1
vote
1answer
57 views

What is the correct idiom for mapping a 0 value in a modulo n expression back to n?

What is the correct idiom for mapping the $0$ value in a modulo $n$ expression back to $n$. For example if I want to be sure that any integer value maps back to the index for a character in the ...
0
votes
0answers
35 views
5
votes
1answer
93 views

Syntax for FrontEnd`SelectionSetStyle

I know FrontEnd`SelectionSetStyle is undocumented, but its name suggests it does what I need. What is its syntax? I have already tried several variations of the ...
0
votes
1answer
79 views

Block Matrix Multiplication [closed]

I have a = {{-1}, {0}, {0}} b = IdentityMatrix[3] c = {a, b} d = {{7}, {2}, {0}, {0}} and would like to compute e = c.d ...
23
votes
2answers
666 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]]] ...
27
votes
2answers
2k views

What are the cool kids talking about when they use ##&[]? [duplicate]

All the cool kids are apparently using ##&[] for Unevaluated @ Sequence[] but I have no idea what either means. ...
0
votes
1answer
69 views

How do I apply a conditional append rule to plot randomly chosen points?

I'm working on an attempt at forming a sort of "Mandelbrot" set using Newton's method and randomly chosen points. Effectively I need to define a loop for Newton's method to determine whether my points ...
3
votes
1answer
133 views

HSQLDB database webserver access

I need a database that runs its connection over http and not tcpip. The "HSQLDB (webserver)" jdbc driver should be able to do just that. The following code launces the webserver but the OpenSQLConnect ...
0
votes
0answers
33 views

What does a single @ do? [duplicate]

I have a simple expression: N@Log2@g[2048] I understand that N is Numerical value , that a function called g is being ran with 2048 as its first argument. But ...
11
votes
1answer
291 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 ...
4
votes
4answers
281 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 ...
1
vote
1answer
27 views

SetterBar Display using MatrixForm

I have vAwGOptns = { {{0}, {0}}, {{1}, {0}}, {{0}, {1}}, {{1}, {1}} }; and would like to select ...
5
votes
2answers
421 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 ...
12
votes
3answers
239 views

Head of a MatrixForm expression?

An example in http://www-zeuthen.desy.de/theory/capp2005/Course/hahn/mathematica.pdf amounts to the following ...
0
votes
1answer
72 views

NDSolve emitting dvnoarg error [closed]

I'm trying to solve this simple system of ODEs, but it gives me the error "The function v1 appears with no arguments". I've attached a screenshot of the code. I hope someone could help me, I really ...
1
vote
0answers
53 views

Using Nearest on a 2D List (seeing extra parentheses)

I am working a problem involving colliding particles. I define a list of particle diameters (effectively a bin distribution). I need to know if two particles collide, in what bin diameter should I ...
2
votes
2answers
149 views

Using list elements as function calls ?

Is it possible to take elements of a matrix or list and use them as arguments of a function? I have a matrix of values, something like this; ...
1
vote
1answer
55 views
0
votes
0answers
33 views

Assigning to a variable with a computed name [duplicate]

I wish to assign about a dozen variables to complicated expressions. to ensure that the correct variable is assigned to the correct expression, I’d like to do something resembling ...
1
vote
1answer
67 views

NestList and RandomChoice from a list of functions

I am tryingg to modify Chaos Game Fractals from Wolfram Demonstrations. The part I am having problem with is this. Original code: ...
0
votes
1answer
44 views

How to get array/list of results of RotationMatrix?

For most other functions, passing in a list of arguments will return a list of results. E.g. t = Range[0, 10]; m = N[Sin[t]] returns ...
28
votes
1answer
765 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 ...
1
vote
1answer
77 views

Ways to protect certain parts of expressions

I am currently working on a quantum mechanics problem where I try to find equations that relate different states of a many-body system. The states are described by sets of pairs of integers, like ...
1
vote
1answer
90 views

Cannot use Part in Pure Function [duplicate]

I need to select some lists in the nested list of form of {{1,2,3},{2,3,4}}. I have used Select to complete my work. But when I tried Position, it doesn't work. For example, ...
1
vote
1answer
377 views

Trying to calculate derivatives of spherical harmonics

I am trying to confirm what is shown on this website: http://functions.wolfram.com/Polynomials/SphericalHarmonicY/20/01/01/0001/ But when I type ...
32
votes
2answers
929 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 ...
2
votes
1answer
107 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
3answers
85 views

Form a matrix to have inequality elements

It looks like a silly question, but I could not find any answers online. Your help is greatly appreciated! Say I have two lists now. ...
5
votes
4answers
328 views
0
votes
2answers
66 views

For Loop in Mathematica {n, factored form of x^(n)-1} for 95<=n<=105

I am new to mathematica. I am trying to write a for loop to print out {n, factored form of x^(n)-1} for 95<=n<=105. I have followed the directions of another for loop, and gotten the following ...
6
votes
6answers
897 views

Can't comment strings with '*)' inside it

I believe it's a bug in notebook's comment parser. I can't comment strings with *) inside it. Something like: ...
5
votes
2answers
243 views

Associativity of `/@` [duplicate]

Why are the following not equivalent: Map[Line, Map[(Print[#]; #) &, {{{2, 1}, {1, 1}}, {{-2, 1}, {3, 1}}}]] which produces ...
3
votes
1answer
112 views

Local evaluation works, CloudDeploy did not work

I a playing around with my programming cloud account. What I have found, interactive functions often are not working because there are several details that are not implemented into the cloud. So I ...
3
votes
2answers
130 views
0
votes
1answer
40 views

Full superset not displayed on Manipulate slider

I wish to incorporate ODE solution with Bondary condition sets: ...
0
votes
1answer
54 views

Help for properly writing simple derivative expression

I need help to write the following expression (only 1 iteration): f(x) = ...some basic function... f[X0,...,Xp] = f(p)(x0) / p! What I have so far: ...
0
votes
1answer
85 views

While Loop Not Looping [closed]

no matter what I do, the following function always returns the first v. This does does not make sense to me at all. It should loop and reevaluate v and only stop when v matches the condition. What am ...
0
votes
1answer
119 views

Position of elements in a list satisfying some criteria - Understanding the syntax [closed]

From this post: if one wants to know the position of the elements of a list that satisfy some criteria, (s)he can do something like that: ...
1
vote
2answers
65 views

How to get the outermost command evaluated first?

I have an expression like ToString[Stuff[...]]. I plan on having the Stuff[...] be manipulated as a string according to the output of other parts of the program. The problem is that Mathematica tries ...
2
votes
1answer
150 views

Array in Sum in Minimize - error “Part specification x[1] is neither a machine-sized integer”

Help please M = 10; z = Array[x, M] {x[1], x[2], x[3], x[4], x[5], x[6], x[7], x[8], x[9], x[10]} ...