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.

learn more… | top users | synonyms

3
votes
1answer
127 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: ...
8
votes
1answer
150 views

Different behaviours of Default Argument

I don't really understand the behaviour of Default Argument. If I execute this command in Mathematica: In: {f[a], f[a + b]} /. f[x_ + y_.] -> p[x, y] ...
0
votes
1answer
399 views

What is wrong with this Cobweb plot [closed]

Something is wrong with my cobweb plot code but I couldn't figure out where do the mistakes come from. So basically we have the iterative map $x_n == x_{n-1}^{2} - 3 \mu$. I would like to draw a ...
3
votes
1answer
174 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 ...
1
vote
2answers
431 views

Translating a “Point-to-Triangle” distance script from MATLAB to Mathematica

Update - Thanks everyone for your responses! After fixing a problem with vector normalization, the code below now works. I'm a new user, and I was attempting to port some Mathematica code from ...
1
vote
1answer
200 views

Solve this equation symbolically

I am trying to solve the equation for the quantity r = y/x symbolically: 3/y^4 == 3/x^4 + a/(x + 2 y)^4 with the requirement that we need to perform the ...
0
votes
1answer
114 views

How to tell Mathematica to make assumptions? [duplicate]

Say I want to integrate 1/(x^2+a^2) and I want Mathematica to know that $a>0$. What would be the command? Something like: ...
3
votes
1answer
94 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 ...
2
votes
2answers
308 views

Write a function that returns the logarithmic derivative

How can we write a function that if we input an expression f, it returns the log derivative $\frac{1}{f} \frac{df}{dx}$. We have to use a conditional or pattern test so that the function accepts any ...
9
votes
2answers
2k views

What does # mean in Mathematica?

I asked Mathematica to compute the following Solve[c (1-x)^2-x^(1/4) == 0, x] and it returned this: x = Root[#1^8 c^4 - 8 #1^7 c^4 + 28 #1^6 c^4 - 56 #1^5 ...
0
votes
1answer
235 views

Mathematica command for type checking?

I have a program where users can enter mathematica commands that can evaluate to any of the standard numeric types (complex, real, int, etc.), or to boolean values. Moreover the users can enter ...
0
votes
2answers
605 views

Why function cannot be defined inside For loop? [closed]

I have a following code (which is simplified version of what I am doing): For[i = 1, i <= 5, i++, f[x_] := Sin[x]^2 Print[{i, f[i]}] ] And the question ...
2
votes
0answers
234 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 ...
6
votes
0answers
106 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 ...
8
votes
1answer
423 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 ...
4
votes
2answers
349 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: ...
0
votes
2answers
77 views

Getting value of clock [duplicate]

I have the following code: a = Dynamic[Floor[Clock[2]]] (*So this basically alternates between 0 and 1*) If[a==1, Print["true"]] But this doesn't work, it ...
1
vote
1answer
169 views

Remove failed Solve[] attempts

I can't figure how to replace a failed evaluation with a null value. I am very new to Mathematica. I have an equation that are being processed using the Solve[] ...
4
votes
0answers
78 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 ...
2
votes
2answers
130 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 ...
1
vote
1answer
168 views

Syntax for integrating over limits specified by a Table

I wish to use NIntegrate to compute multidimensional integrals. However, I don't want to manually input the limits for the dimensions. I want to store the ...
5
votes
3answers
520 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
0answers
105 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: ...
8
votes
5answers
544 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 ...
7
votes
3answers
326 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 ...
5
votes
2answers
218 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 ...
1
vote
1answer
97 views

When is Evaluate needed within function arguments? [duplicate]

I'm trying to do a simple variable substitution within a ContourPlot, but it's not working. Here's an example: ...
10
votes
2answers
267 views

Functions that remember their values

Can someone explain what is going on with the following ... func[y_] := func[y] = (Print["Hello world !!!"];) func[1] Hello world !!! ...
1
vote
3answers
340 views

More than one expression in the Table[] command?

I would like to construct a Matrix using the Table[] command. The issue is that I would like to use more than one expression for it. What I need to obtain is something like this : ...
7
votes
2answers
264 views

What's the purpose of the Unique function?

As the title says: What's the purpose of Unique? I understand that it generates some unique symbol, but when and for what is it to be used? Are there applications ...
3
votes
2answers
190 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 ...
1
vote
1answer
207 views

Syntax error: newline character interpreted as multiplication

I'm getting this error in Wolfram Workbench, and I don't know where it comes from: "Syntax error: newline character interpreted as multiplication" This error happens around an If[] function, in a ...
4
votes
2answers
202 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 ...
6
votes
1answer
600 views

Coding mistake? [closed]

I have just started using Mathematica with v9.0. I am trying to follow a computation from a book on Fourier series with the function $f(x)=x$ on the interval $-\pi < x < \pi$. Here is the code ...
10
votes
1answer
500 views
23
votes
1answer
576 views

Convenient string manipulation

With Mathematica I always feel that strings are "second class citizens." Compared to a language such as PERL one must juggle a lot of code to accomplish the same task. The available functionality is ...
9
votes
2answers
521 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: ...
3
votes
1answer
86 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 ...
2
votes
0answers
178 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 ...
10
votes
3answers
765 views

Working with PhysicalConstants

I recently found the PhysicalConstants` package. First I thought this was nice, since I didn't have to look up some quantities all the time and copy them into the ...
10
votes
3answers
313 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 ...
19
votes
2answers
1k 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
105 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
616 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: ...
1
vote
1answer
119 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
191 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
175 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
137 views

Problem overloading D[] using UpValues

First I define an entry of UpValues overloading D[] for expressions with head ftest: ...
0
votes
1answer
150 views

How to generalize a formula?

This is a piece of my code: ...