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.
6
votes
1answer
103 views
Problem overloading D[] using UpValues
First I define an entry of UpValues overloading D[] for expressions with head ftest:
...
6
votes
0answers
91 views
Design considerations behind `O` (a.k.a. BigOh, a.k.a. Landau Order)
This works without any warnings: O[Log[x]].
This raises a warning: O[x^2].
I have a few questions around this:
Why is it a ...
5
votes
4answers
255 views
Multiple colors in Graphics[] environment
There are other questions on the site that are similar to this one, but the answers provided didn't help me.
I want to draw disks of different radii. Each radius is the absolute value of a variable, ...
5
votes
3answers
149 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?
5
votes
2answers
133 views
Splicing a list of arguments into a function with Sequence
Not sure if this has been asked, but I have a fairly simple operation that I don't know the syntax for. Say I have an array with some values, and a function f that accepts an arbitrary number of ...
5
votes
1answer
170 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. ...
5
votes
1answer
236 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 ...
5
votes
2answers
320 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:
$$
\sum_{d=1}^{P}e^{-d}\sum_{\substack{1\leq k_{1}\leq Q \\ 1\leq k_{2}\leq Q \\... ...
5
votes
2answers
215 views
Extracting parts of nested lists of rules using a syntax similar to JsonPath or Xpath
Given an example data set:
...
4
votes
3answers
158 views
Is it possible to make the Button execute two or more actions?
According to the help:
Button[label,action]
Is it possible to make the button execute two actions?
4
votes
2answers
275 views
List reversion inspired by Python
In python, if you wish to reverse a list, here is the trick:
range(10)[::-1] => [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
Note: ...
4
votes
3answers
138 views
Keep function range as a variable
Plot[2*x^2 - x + 2, {x, -1, 1}] plots a function of x from -1 to 1. As far as I can see, I cannot "save" this range in a variable:
...
4
votes
3answers
160 views
Brackets in output make unable to use output to identify matrix element
I'm trying to write a code where each matrix element swaps with a randomly selected neighbor (cardinal directions only) to redistribute the matrix. So far I've been able to replace an element with its ...
4
votes
1answer
291 views
What is the difference between Set and SetDelayed?
I have a problem with defining a function and most of time I get confused by Set or = and ...
4
votes
2answers
271 views
Evaluating an If condition to yield True/False
I would like to decide whether an option passed to my custom function has the value Automatic or something else. This is my attempt:
...
4
votes
3answers
306 views
Integrating with multiple indicator functions
I am trying to calculate an integral involving multiple indicator functions, such as:
$$ 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)\, ...
4
votes
1answer
68 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 ...
4
votes
2answers
117 views
How can I compare the previous value and the current value implemented during NestWhileList?
I am trying to write a part of my code. I am using NestWhileList. However, I couldn't find out the right syntax for testing. It should compare previous result and current result and continue if it is ...
4
votes
1answer
183 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
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
1answer
75 views
How do you set an Optional parameter with a global variable on a Function defined in a Package
In a Package I am writing, I'm trying to define a function with an Optional parameter in it that is set to a global variable.
...
4
votes
0answers
55 views
Is there a way to check whether two notebooks share the same variables?
When I code in Mathematica, I often re-use code from old notebooks which fulfilled a specific purpose; for example, one testing for soft matches in strings, or one that identifies outliers on a graph ...
4
votes
0answers
78 views
Proper treatment of roots and powers in Series?
I have the following problem in Mathematica 9 on Linux. I let Mathematica compute the Series expansion:
...
3
votes
5answers
255 views
Using variables in function names
I want to make a list of plots and my functions are named C1, C2... Cn.
The command I wish ...
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:
...
3
votes
1answer
76 views
Syntax Coloring for “Possible Unwanted Assignment” Issue
Apparently Mathematica's syntax coloring engine believes that the second assignment in the following code excerpt (concocted for illustration purposes only) is a "Possible Unwanted Assignment" since ...
3
votes
1answer
114 views
Using single replacement rule to convert algebraic expression
I have been trying this problems for hours and cannot find any helpful clues.
How can I convert $Sinh[3\theta]+Sinh[\theta]$ to a rational function of x given $2Sinh[\theta] = x-x^{-1}$ by using only ...
3
votes
1answer
67 views
Dt acting on symbolic notational forms
This one must be simple, but I can't figure out a decent solution.
Suppose, I have a symbol with a notational form applied to it, say OverHat[A].
Now, if I didn't ...
3
votes
2answers
124 views
How to remove border points from InputForm?
I have this code, and it generates the below ListStreamPlot. The second graph is the ListStreamPlot overlaid with the points ...
3
votes
1answer
79 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 ...
3
votes
1answer
240 views
Explanation on why Compile statement works only if input and output sizes work
I found the following code:
Compile[{{m, _Real, 2}}, Fourier[m]][Table[N[i - j], {i, 4}, {j, 4}]]
which doesn't work correctly. But the following was posted as a ...
3
votes
1answer
111 views
Filtering the elements of an array to split them into two categories
So, I am new to Mathematica, and I am trying to write something that involves taking values from one array and separating them into two different arrays. My code for doing this is:
...
2
votes
2answers
255 views
Single dot textual form
How do I render a letter with a single dot above it?
I see \[DoubleDot] and \[TripleDot] are readily available, but what about ...
2
votes
3answers
577 views
Orthonormalization of non-hermitian matrix eigenvectors
When using Orthogonalize[] one can specify which definition of "inner product" is to be used. For example, ...
2
votes
2answers
101 views
How to make Mathematica returns the exact expression I typed
I'm using Mathematica to compare some constants. Before playing around with those constants, I would like to check that I didn't make any mistake in typing them. So my question is the following: "What ...
2
votes
3answers
234 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.
...
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:
...
2
votes
4answers
244 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
2answers
191 views
local variable naming & symbolic argument
I'm stuck here with my variable assignment in this scenario
...
2
votes
3answers
143 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 ...
2
votes
1answer
224 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:
...
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?
...
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 ...
2
votes
2answers
514 views
NMinimize with defined function call getting error NMinimize::nnum
I want to call the NMinimize function for my own defined calculations but I got an error. Below is a simple example.
...
2
votes
1answer
159 views
Why does the first derivative of a piecewise continuous function turns out with discontinuities?
I have this piecewise continuous function which is also continuously differentiable over time :
...
2
votes
2answers
361 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:
...
2
votes
0answers
75 views
Conditional statements in intial conditions?
This is potentially a daft question, but I thought I'd ask it; I have some material free to diffuse in a boundary between rn and ro; I've been able to get it working nicely for neumann type boundary ...
2
votes
0answers
73 views
Transfer of symbols between contexts
As many others (I guess) I'm struggling with the handling of contexts within Mathematica. I'm working on a new package definition with the usual syntaxt specified by the Mathematica documentation:
...
2
votes
0answers
117 views
Syntax colouring when using Symbolize
I need to use symbols with suffixes in order to make my code readable in relation to the Eurocodes. To do this I use Symbolize from the ...
1
vote
2answers
179 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 ...
