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.
7
votes
3answers
192 views
how to read in a file in the same directory?
Now I am writing a small package. I have written several files and put them in the same directory. And some files need to read in or include another file in the same directory. But when I simply write ...
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
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:
...
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:
...
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
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 ...
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 ...
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:
...
17
votes
2answers
625 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 ...
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:
...
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
...
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 ...
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
...
8
votes
5answers
300 views
can the color in MeshStyle be specified by a ColorFunction, such as “SunsetColors” for example. If so, what is the correct syntax?
This is an example given in Help:
Plot3D[Sin[x y], {x, 0, 3}, {y, 0, 3}, MeshStyle -> Gray]
Could this be changed to something like
...
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:
...
8
votes
2answers
259 views
How can one define an infix operator with an arbitrary unicode character?
You can setup "UsefulFunction[a, b]" to use custom infix notation "a [LeftRightArrow] b" as follows:
...
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 ...
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
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:
...
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 ...
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 ...
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 ...
5
votes
2answers
316 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:
$$
\sum_{d=1}^{P}e^{-d}\sum_{\substack{1\leq k_{1}\leq Q \\ 1\leq k_{2}\leq Q \\... ...
3
votes
1answer
76 views
Syntax Coloring for “Possible Unwanted Assignment” Issue
Apparently Mathematica's syntax coloring engine believes that the second assignment in the following code excerpt (concocted for illustration purposes only) is a "Possible Unwanted Assignment" since ...
11
votes
3answers
204 views
Numbers in alternate bases transcend the evaluator?
It looks to me like a number in a base other than base 10 gets evaluated before the evaluator ever gets a chance to be tweaked.
For example, FullForm[16^^abcdef] ...
5
votes
1answer
168 views
Why does the Front End group backslashes into pairs?
What is \\ for? Help finds nothing on it. An odd number of backslashes greater than one are grouped by two and the last one is displayed with a different color. ...
10
votes
4answers
293 views
Extracting equations from Piecewise expressions
Say I have a PDF:
PDF[LogNormalDistribution[1.75, 0.65], x]
Calculating it, Mathematica gives me an expression that looks like this:
I want to extract the ...
7
votes
3answers
266 views
Why can't D[] be used in place here? [duplicate]
Possible Duplicate:
General::ivar is not a valid variable when plotting - what actually causes this and how to avoid it?
Beginner question:
Why can't I use ...
8
votes
1answer
134 views
Accept Infinity as an Integer argument
I have the following function, albeit contrived:
Foo[x_Integer] :=
Module[{i},
i = 1;
While[i <= x && i <= 10, i++];
i - 1
];
I am ...
8
votes
2answers
176 views
Cases[data,Colon[key,_]] vs. Cases[data,key:_] toward XPath, XQuery
Exploring methods to index and search tree-structured key:value pairs via named-entity index (key paths) as opposed to Position-based indexing.
Using Rule as ...
4
votes
3answers
305 views
Integrating with multiple indicator functions
I am trying to calculate an integral involving multiple indicator functions, such as:
$$ 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)\, ...
7
votes
5answers
1k views
Notation of partial derivative
I want to write partial derivatives of functions with many arguments. Why is it that when I type
f[x,y] ctrl+6 (0,1)
it turns out to be bad syntax? The output of
...
2
votes
3answers
573 views
Orthonormalization of non-hermitian matrix eigenvectors
When using Orthogonalize[] one can specify which definition of "inner product" is to be used. For example, ...
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 ...
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:
...
2
votes
2answers
509 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.
...
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.
...
11
votes
7answers
396 views
Equating matrices (or higher order tensors) element-wise
Say I have two matrices (or, as in my case, higher order tensors) $A,B$, and I want to solve the equation $A=B$. To do so , I need a list of equations that equate entry-wise the elements of $A$ and ...
8
votes
4answers
306 views
Error when using rule as a list index - { i, x[[i]] } /. i -> 5
I can't seem to use a rule to index a vector.
x = Range[10];
{ i, x[[i]] } /. i -> 5
I get the following error when evaluating the above code, even if the ...
8
votes
2answers
456 views
Collapse a section of a huge function
(I have recently taken to Mathematica... still a noobie)
Is there an elegant way of hiding/collapsing only a portion of a function (for example, in Matlab, within a function, one can collapse the for ...
