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.
10
votes
3answers
262 views
Why does ++++x return an increment of 2 when the value of x is only incremented by 1?
This line returns 3:
x = 1; ++++x
However, the value of x after the increment is only ...
17
votes
2answers
623 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 ...
3
votes
1answer
78 views
Force ellipsis to print an end of an expression
For pedantic reasons I want to display an infinite sum of fractions in fractional form (i.e. as 1/x not as x^(-1)) with an ellipsis at the end of the expression. I have tried a number of ways and ...
2
votes
2answers
360 views
Several functions in one RegionPlot with different grayscale
I try to plot the following, but something seems to be wrong in my code and I can't figure out how to fix it:
...
39
votes
2answers
776 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 ...
1
vote
1answer
96 views
Working of Date[]
Date[] returns the current date of local system, Date[1] returns {2012, 11, 15, 17, 41, 0.3161629}, ...
2
votes
1answer
154 views
Difference between Map[f[#] + g[#] &, {a, b, c}] and Map[f[x]+g[x]&, {a, b, c}]
Map[f[#] + g[#] &, {a, b, c}] vs Map[f[x]+g[x]&, {a, b, c}]
My question is: why is the output different?
...
11
votes
3answers
144 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. ...
6
votes
1answer
103 views
Problem overloading D[] using UpValues
First I define an entry of UpValues overloading D[] for expressions with head ftest:
...
0
votes
1answer
127 views
4
votes
1answer
67 views
Setting a binary operator Flat
I defined a binary operator in as the first statement in a new Mathematica notebook.
{x1_, y1_} ⊕ {x2_, y2_} := Module[{}, Print["do anything"];]
where the code ...
2
votes
2answers
189 views
local variable naming & symbolic argument
I'm stuck here with my variable assignment in this scenario
...
7
votes
3answers
266 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 ...
1
vote
2answers
199 views
How to insert an expression in a Mathematica program?
I need to insert a very large expression in a Mathematica program. So I first
Put[large expression,"file"]
and then use
Block[{}, Get["file"];...]
to ...
2
votes
2answers
270 views
Superscript prime symbol
x\[Prime] looks like $x_'$, ugly right?
Is there a way to make a symbol with prime to look like $x'$?
That's what I'm trying right now:
...
0
votes
0answers
164 views
Derivatives in scripts [closed]
I have consistently been harrowed by this tiny issue.
When I Try to run my Mathematica script, I get this error message:
...
4
votes
1answer
182 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 ...
1
vote
1answer
277 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"?
2
votes
3answers
141 views
How do I interpret the following syntax?
I have been given some code with the following line
PeriodicExtension[g_, x_] := If[Abs[x] < Pi, g[x], PeriodicExtension[g, x - 2 Sign[x] Pi]]
I do not ...
6
votes
1answer
162 views
How can I specify a numerical order for variables?
I need to specify that a variable is less than another, and greater than yet another, in a Mathematica program, because I will later apply a test to them that will determine what functional form to ...
4
votes
1answer
250 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
2answers
270 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:
...
4
votes
1answer
285 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 ...
10
votes
4answers
293 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 ...
5
votes
2answers
215 views
Extracting parts of nested lists of rules using a syntax similar to JsonPath or Xpath
Given an example data set:
...
15
votes
3answers
609 views
Why does Mathematica use [[ ]] notation for array indexing?
I am confused by why Mathematica uses [[3]] to get the 3rd element, or [[i,j] to get the i,j-th element of a 2D array.
This ...
6
votes
2answers
152 views
Internal Representation of ?name and ??name
Code
FullForm[Hold[?name]]
Syntax::bktmcp: Expression "Hold[?name]]" has no closing "]".
Syntax::sntxi: Incomplete expression; more input is needed .
Question
...
16
votes
1answer
277 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 ...
4
votes
3answers
158 views
Is it possible to make the Button execute two or more actions?
According to the help:
Button[label,action]
Is it possible to make the button execute two actions?
1
vote
1answer
177 views
Can I use Table without the appropriate bounds?
I´d like to use the Table command without defining n, so that I can have a list of n ...
2
votes
3answers
232 views
Output of plots from within Do[ ] Command
I am wondering why the following does not plot the way it's written and exactly how does the Do[] function operate? I think I could be using it incorrectly.
...
9
votes
4answers
227 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
...
14
votes
2answers
262 views
Distributing PlusMinus consistently
I would like to give the built-in function PlusMinus, which is undefined by default, the intuitive meaning: considering all possible combinations of $+$ and $-$.
...
2
votes
4answers
242 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
...
2
votes
1answer
222 views
Indices and variable definitions in Mathematica
Does anyone know how I can do this in Mathematica? Just an example..
Defining indices and variables (defined over indices), "mapping" variables and indices:
...
12
votes
4answers
937 views
Clear complains that a variable is not a symbol or a string?
Here's a small listing where I've used EscqEsc to typeset θ in the notebook:
...
11
votes
2answers
224 views
Convert operator to string
How to programmatically convert an operator such as Equilibrium into its displayed form as a string? The conversion should work like this:
...
11
votes
3answers
204 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] ...
7
votes
2answers
153 views
“A number in base b” and pure functions: why doesn't b^^# & work?
Why do the following not work (in Mathematica 7)?
2^^ # & /@ {1000, 1101}
and
2^^ # & @ 1101
This does work:
...
2
votes
1answer
168 views
What is an alternative to using backticks in separating namespaces from function names?
What is an alternative to the backtick (`) in separating the namespace from the function name?
Can the function be called without using this symbol? I think in ...
7
votes
1answer
229 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 ...
4
votes
3answers
305 views
Integrating with multiple indicator functions
I am trying to calculate an integral involving multiple indicator functions, such as:
$$ h(u,v,w) = -\int_0^1 J^{\prime\prime}(s) (I_{(0,s]}(u) - s)(I_{(0,s]}(v) - s)(I_{(0,s]}(w) - s)\, ...
6
votes
3answers
461 views
Using D to find a symbolic derivative
I need to do the following:
Define a function
Take the derivative of this function and have a look at the symoblic representation
Substitute in some values
With the bonus that I want to use the ...
5
votes
3answers
147 views
Syntax for prefix mode with multiple arguments using @ shorthand
Is it possible to use the @ symbol with multiple arguments? The Prefix command suggested not. If so, why?
3
votes
4answers
1k views
Mapping multiple parameters of a function to specific values
I am a little bit confused by the documentation for Apply (@@).
I want to define a list of parameters, for instance:
...
1
vote
2answers
178 views
Finding the position of a specific value in a list
Is it possible to easily find the position of a specific value in a list? For example, if the list is {{x1,y1},{x2,y2},...,{xn,yn}} I would like to know the ...
5
votes
1answer
168 views
Why does the Front End group backslashes into pairs?
What is \\ for? Help finds nothing on it. An odd number of backslashes greater than one are grouped by two and the last one is displayed with a different color. ...
10
votes
2answers
97 views
Functions in a different context are replaced with infix forms of their namesake in System`
So, in an attempt to help out Fabian with his question, I did what I often do, and created a new symbol in the Pillsy` package that I could play with. Since it was ...
0
votes
1answer
221 views
What does the slash-colon symbol do?
I came across a bit of code that uses the syntax /: and I don't know what it does. I can't find its documentation, or maybe I'm just not looking properly. The code ...
5
votes
2answers
315 views
Constructing a Summation with a Variable Number of Inner Sums
I have a question regarding multiple sums. And my second index depends on the first index. Here it is:
$$
\sum_{d=1}^{P}e^{-d}\sum_{\substack{1\leq k_{1}\leq Q \\ 1\leq k_{2}\leq Q \\... ...
