# Tagged Questions

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.

303 views

### Limit won't compute

Does anyone know why the limit: ...
367 views

### Finding the square root of a squared number?

Taking the square root of the square of a number Variable set to a real value I'm wondering why these examples a = -4.3; Sqrt@a² Sqrt@(a^2) Sqrt[a^2] Sqrt[a²] ...
394 views

### Treat all variables as local in a module [duplicate]

In most languages, any variable defined inside a function is considered local. ...
146 views

### Why does the iterator index in Table not work here?

I type the following command line Table[D[#1,varx[[i]]] &,{i,3}] where varx is a vector of dummy variables ...
470 views

### import a list of replacement rules

I have a text file with a set of replacement rules, of the form x^3y^2 -> 4, xy^2 -> 2, ... for example. I'm having some issues trying to figure out ...
79 views

### Decapitating “explicit” and “implicit” heads

This is a follow up to this question. So far, I named "explicit" heads to those that appear explicitly in the expression. For example, f[x] has an explicit head. I ...
2k views

### Difference between @ and @@

I am confused by the commands @ and @@. From the documentation, I learnt that @@ is the ...
264 views

### Syntax error for optional pattern, but only in debugger

This expression (explained here by Leonid) evaluates fine unless Evaluation->Debugger is enabled: h[x : (_Integer) : 1] := x Syntax::sntxf: "x:" cannot be ...
44 views

### Matching Root[…] objects with patterns, unexpected hidden argument

I needed to write patterns that could distinguish between arbitrary-function and polynomial forms of Root objects, for example, ...
147 views

### Defining an operator

Let s be a positive integer and let DifferenceDelta be this function with step = 1. Define <...
94 views

### Plot producing many error messages when given complicated function

I'm new to Mathematica and am running in to all sorts of silly difficulties with coding in it. I'm trying to calculate a function f[x, k], normalise it with another ...
267 views

### Where did I go wrong with my implementation of finding a plane tangent to a surface?

I am working on finding the plane tangent to a paraboloid at a given point. My code: ...
129 views

### Why only up to two \[Prime] superscripts are interpreted as derivatives?

I noticed that only up to two \[Prime] superscripts are interpreted as derivatives. Is there a reason for this restriction? Is it documented? ...
366 views

### Where did I go wrong with my implementation of the trapezoidal rule?

One method for doing quadrature, called the trapezoidal rule, improves accuracy by connecting the points on the curve corresponding to the points of subdivision with line segments, forming trapezoidal ...
198 views

### Shortcut for Range[]?

I use Range a lot. Is there any syntactic shortcut for it, or do you always have to spell it out?
122 views

### Passing f[x][[1]] to FindRoot [duplicate]

FindRoot seems to fail for most examples of the form f[x_?NumericQ] := {x - 3 , x^3}; FindRoot[f[x][[1]], {x, 3}] ...
95 views

### Syntax for FrontEndSelectionSetStyle

I know FrontEndSelectionSetStyle is undocumented, but its name suggests it does what I need. What is its syntax? I have already tried several variations of the ...
103 views

### Is it possible to use a mathematical expression as function name?

This might seem as a silly question, but is it feasible to use a mathematical expression as the name of a function? For example, I'm studying the cross section of Compton scattering and there is a ...
121 views

### Help with writing a polynomial series [duplicate]

I want to write and evaluate an expression something like Sum[x[i] Product[y[j], {j(!=i), 1, n}], {i, 1, n}] but with correct syntax, where n is a any number (...
99 views

### Where does Documentation Center introduce the basics?

While helping a user who mistakenly thought that log rather than Log was the correct built-in function name, I included a gently-...
193 views

### Levels and slots

I am struggling with levels and #, if I understand this I think I will be able to grasp the entire concept. ...
323 views

### Manipulate, Import external table, save as CDF, mail presentation

For my work I do data analysis. Most of these analysis are done on big databases with milions of records. I would like to make a manipulate (or animate) using a external dataset and create a CDF ...
270 views

### HoldForm[Operator ##] on some list

Recently in response to this question Mr.Wizard suggested an unusual way to summing numbers. This doesn't seem to be documented. ...
5k views

### Guidelines on giving readable names to variables [closed]

I know that one cannot use underscore to a variable name, like degree_of_The_First_Polynomial. But for a long variable name, it ...
152 views

### The /. syntax in numerical methods [duplicate]

I have an analytical approximation method for solving an ODE and want to compare this to an NDSolve solution, but the syntax is confusing me. To get the solution from NDSolve, I define the ODE as eqn ...
1k views

### How is + as an infix operator associated with Plus?

How is + associated with Plus? Suppose I want to define a head FooBar and have it ...
422 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 ...
115 views

### Assign variables from list inside With or Module

I have found that it is possible to assign variables from lists, as follows. r = {1, 2, 3}; {a, b, c} = r; b 2 However, ...
205 views

### Constraint syntax compaction

Is there a more compact way to represent these constraints: NMaximize[{a+b+c,a <= 5 && b <= 5 && c <= 5...
295 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 (...
339 views

### Writing a function that returns a (usable) function

I am trying to create a function that returns Arnold's Cat Map of size n iterated k times. I can get something out of the Function command, but I can't figure out ...
955 views

### What is the right way to construct DynamicModule

When I'm creating DynamicModules for CDF purposes I'm usualy basing on my experience with that, particular goal and content rather than on deep insight. I want to ...
79 views

### Why do two codes give different output?

I have tried the following to get the eigenvalues of several matrices of the type: ...
82 views

### Constructing an Array from typed expression

I want to produce an array from expressions given by test[one][1] = 3; . . test[one][5] = 7; etc. Normally would use ...
118 views

### How to make InverseFunction work on function defined with restriction on arguments

This example works to define InverseFunction on the first argument of a function ...
271 views

### Overlapping pure functions

Let say I need and option for Plot: RegionFunction -> (-6 < #2 < 6 &) But I also want those ...
467 views

### Split dataset based on the first column [duplicate]

I have a dataset which I want to split based on the first column. The data looks like this ...
166 views

### Equation values into list

Suppose I have a function say $f=x^2$. What I would like is a list (or even better, a list with a grid) which resembles {{1,1},{2,4},{3,9}, ...}. Ideally one should ...
932 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 ...
220 views

### DeleteCases vs. DeleteDuplicates for removing points within a critical Euclidean distance

I'm attempting to remove all points in an array which are within a Euclidean distance "ThresDist" of one-another. Using the command: ...
638 views

### Constructing symbol definitions for With

I would like to be able to define two arrays, one containing symbol names and one containing the values of those symbols, for use in constructs such as With. For ...
455 views

### How to get 'exact' expression for result

I have a result from Mathematica for which want to have the exact expression, i.e. all of the arguments of type # replaced. It is given by: ...
232 views

### Correct usage of GeoPosition

My goal is to trace a ray down to the ground. I have done: ...
187 views

### Shortening the syntax {var1, var2} /. # & /@ list

I noticed that I often turn out to have a list of substitutions in the form ...
179 views

### Extracting counts of contiguous zeros and ones from a binary array

I'm a novice with Mathematica, but you guys have been very helpful to me in the past. I have a binary array [100, J repetitions] consisting of zeroes and ones. I'd like to extract a histogram of the ...
252 views

### Bincounting a list

I'm a Mathematica novice here. I'm trying to execute the following code to add random 1's into a zero matrix, repeat this many times, and then bin/histogram the number of nearest neighbor 1s. Can ...
112 views

### Export file with semicolon at the end of line

Is there a rule that tells Mathematica to set a semicolon at the end of each line (except of the last one)? My MWE is: ...
2k views

### What do the hashtags represent in the result of Solve, and how should I use them? [duplicate]

There is a function that I'm trying to get the inverse of. My function is a simple polynomial: Tn[T_] := 4/9 T^3/Tc^2 + 5/9 T Now I tried to find ...