For questions on writing functions (pure or using Set/SetDelayed) for any purpose, including the features that may be incorporated in those functions, such as options, patterns and conditions.

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0
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0answers
43 views

Greatest common denominator command. Can you explain why this command works?

Can you explain how this function works? mysteryFunction := Fold[#/#2 /. {n_~_~_ -> #/n, _ -> #2} &, #, {##}] &
7
votes
2answers
3k views

Module with “local functions”

I am trying to use a Module having "local functions", i.e., those which I need to define only inside this module. So I tried this: ...
3
votes
0answers
58 views

Custom units Compatible with Conversions [closed]

I am writing a Mathematica Palette to work with units, and am wondering if anyone knows a way to define new units outside of the standard ones that come with Mathematica 9. I do know of the ...
5
votes
2answers
279 views

Simpler way to type Derivative[1, 0][u][0, x]

Though not unbearable, I always feel a little nervous when typing partial derivatives at a specified place e.g. $u^{(1,0)}(0,x)$, which happens a lot when setting initial/boundary conditions for PDEs. ...
0
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0answers
36 views

How to define a general linear function [duplicate]

I'm trying to work with a general linear function in Mathematica. I would like to assign some sort of rules to a function, say Tbar, to evaluate linearly. Basically what I would like to do is have ...
1
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0answers
37 views

Getting a list of function definition parameter values [closed]

If I define a function over certain values: f[0] = 1 f[1] = 2 f[2] = 3 How do I get the list of parameter values that it's been defined on? ...
2
votes
1answer
121 views

Syntax f[x_][y_]

Need to understand the principle of the distinction between f[x_,y_] and f[x_][y_] It seems also that z[x_, y_][a_, b_, c_][α_, β_] := a (x + y)^b + c/(α-β) ...
1
vote
0answers
62 views

Distinguish hashtag # operator when using multiple functions [duplicate]

I would like to do this list = Append[list[[#]],Map[list2[[1, #]] & , list[[#, 4]], {2}]] & /@ Range[Length[list]]; But I would like to substitute ...
1
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1answer
62 views
21
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1answer
476 views

How can I export my learned ClassiferFunction[] and PredictorFunction[]s?

Mathematica 10 provides beautiful high-level machine learning functionality. Sadly, the learned functions once created are rather opaque objects. I need to use them in other projects, so here is my ...
21
votes
7answers
1k views

Using patterns in pure functions

Pure functions may be handy if you don't want to assign your function a name. For example I would calculate $x(x-1)$ for some numbers $x$ by ...
9
votes
1answer
180 views

How to construct the RHS of Wick's theorem

I've been trying this for a few days now, but I just can't seem to find an efficient (speed-wise) functional way to code the following task. Context: I would like to construct an expressions that is ...
6
votes
1answer
34 views

How is Attributes protected and yet can still be set?

The Attributes function itself has the attributes: Attributes[Attributes] ...
9
votes
6answers
476 views

How to generate this structure of a list without `While` and the like?

I need to create a list that holds, for given integer d, the elements $1,\ldots,d,d+2,\ldots,2d,2d+3,\ldots,3d,3d+4,\ldots,d^2$ where $\ldots$ is just denoting ...
5
votes
3answers
174 views

Number by permutation

I want a function that compute number of permutation in lexicographical order. E.g. ...
2
votes
1answer
165 views

Passing function as argument

I've been mucking around with passing functions as arguments to other functions and via trial and error seem to have something that works. I was wondering if someone could have a quick look at some ...
1
vote
1answer
38 views

Plot is empty (probably) due to poor function definition

I am trying to plot my response $x(t)$ as a function of system parameter $M_0$. Here is my code to regenerate my problem ...
1
vote
2answers
103 views

n fold convolution of a function via a recursion function

I wanted to write a recursion function to calculate the n-th convolution of a function f[x_]. I wrote the function ...
7
votes
2answers
165 views

Sets and sums of different elements

Consider the set S={w,x,y,z}. If the set of all possible sums of any three different elements from S is {-1,3,5,8}, then what is the set S? How could I solve this function using Mathematica?
8
votes
2answers
98 views

For loop works at top-level but not in a function

Why does this work: For[i = 1, i <= Dimensions[list][[1]], i++, list = Insert[list, i, {i, 3}]] But this doesn't: ...
5
votes
1answer
76 views

How to obtain the Derivative of a pure Function of variable number of arguments?

Here is a function f that takes a variable number of arguments: f = Times[##]*Log[1 - Times[##]] & I now want to ...
0
votes
1answer
92 views

How to turn a subroutine into a function?

I've written a subroutine that takes in 6 matrices and after some manipulation returns back 3 new ones. I will use this subroutine fairly often in this notebook so I think it would be easier to turn ...
4
votes
2answers
100 views

How do I localize an assignment to expression (instead of symbol) within scoping construct?

Is it possible to localize an assignment to an expression (defined via UpSet) instead of a Symbol within a scoping construct? ...
0
votes
0answers
48 views

How to calculate a continuous function once and access values later?

I have a function that involves a numerical calculation: h[v_]:=NIntegrate[f[x]*Log[p[x, v]], {x, -Infinity, Infinity}] I need to visualize how well a bunch of ...
1
vote
1answer
52 views

AbsoluteTiming of nested integration gives strange result

I found somewhat strange behaviour of nested integration timings. Consider the following code: ...
1
vote
1answer
96 views

Plotting a periodic function [duplicate]

My question is the following: how can I plot a function repeatedly? By following some topics here I found some basic information about using Fourier series. This is what I made: ...
0
votes
1answer
41 views

Why doesn't this function definition work?

I am trying to define a following function (which is a convolution integral) ...
2
votes
2answers
113 views

How to set a values inside a custom function [duplicate]

I have a custom function like this stringLength[string_] := StringLength[ ToExpression[StringJoin[ToString /@ {del, string}]] = StringDelete[string, " "]] ...
1
vote
2answers
70 views

Finding roots of a function that includes Bessel functions [duplicate]

I'm fairly new to Mathematica so forgive any stupid mistakes. Here's my function: ...
0
votes
3answers
80 views

Write complex number in terms of absolute value and phase

I have a long vector and some of the values (19 out of 64) are complex. I got them using the Mathematica Rationalize function, so the complex ones are written in the a+bi form. Is there a function I ...
0
votes
0answers
59 views

Considering special cases in general definitions

I want to calculate some coefficients $\qquad B_k = 2\int_0^1 u(x) \cos(k\pi x)\,dx$ for $0<k\in\mathbb N$ and I am doing this in the following way: ...
18
votes
3answers
383 views

Writing functions with “Method” options

I'd like to implement several behaviors for a particular function using a Method option added to the function definition: ...
0
votes
0answers
56 views

break down the function

I am using Series function, but I found that it cost too much time. Since the Series function is Taylor expansion and I only need first order, I want to break down the code, so I can make it faster <...
1
vote
2answers
86 views

Partial Function Evaluation [closed]

How can I evaluate only part of a stack of function calls? In particular, given f[x_,y_,z_]=x+y+z;, say, I'd like to define a function ...
2
votes
1answer
48 views

Passing a list to a nested vector function

In order to apply a newton-rhapson algorithm to solve a set of nonlinear vector equations such as these, f[x_, y_] = {x^2 - 3*y + 6, (y + 1)^2 - x - 33} I need ...
5
votes
4answers
96 views

Multi-index variable depending on signature of permutation of indices

I do have some multi-indexed variable, e.g. like this \begin{align*}f_{123} &= 1\\f_{345} &= 1/2\end{align*} where $f$ is antisymmetric under permutation of any pair of indices, i.e. e.g. $...
1
vote
1answer
39 views

How to use Composition when the functions have two parameter

There are some basic instructions about Composition on this site, but I'm still confused on how to use it when the functions I am composing have two parameter, such ...
3
votes
2answers
255 views

Why can't FindFit get the proper result in this problem?

Cross-posted in http://tieba.baidu.com/p/4425634583 The mathematica helps me solve one differential equation in numerial method and got the data of the answer,but the taylor series fit is not good in ...
3
votes
4answers
3k views

How to write a differential operator in Mathematica

I have a very basic question. I am trying to code the LHS of the differential equation: $$\Big[\frac{1}{\sin\theta}\frac{d}{d\theta}\big(\sin\theta\frac{d}{d\theta}\big)-\frac{m^2}{\sin^2\theta}+n(n+...
4
votes
1answer
65 views

How to use currying to write a tail recursive function for summing factorials given a certain bound

I am very confused about how can i use currying to write a tail recursive function for summing factorials within a certain bound or summing the bounds i.e. given [1,5] i should be getting 1!+2!+3!+4!+...
3
votes
1answer
71 views

Mod[k, 2] == 0 versus EvenQ[k] [duplicate]

I'm having some trouble with Mod[k, 2] == 0 versus EvenQ[k] They are sometimes yielding different results when given the ...
0
votes
1answer
46 views

ND on a function using NIntegrate

I need to numerically differentiate a function that takes a list as an argument and that uses NIntegrate in its definition. A simple example is ...
4
votes
1answer
91 views

Writing a function that finds the difference between two maxima

Suppose i have two functions: $\qquad -2x^2 +5x+3$ and $\qquad -5x^2 +2x+3$ To solve the point where the functions are at maximum i use the command NMaximize ...
4
votes
1answer
120 views

Jackson Integral

Following an old post, I have tried to make a function that calculates the Jackson integral of $q$-calculus: ...
4
votes
1answer
220 views

How to Override the Head of a Symbol

I was wondering if it is possible to override the head of symbols/operators. As a motivating example if I run: Then Ket will be returned. But lets say I want Bob to be returned instead of Ket. Is ...
0
votes
1answer
42 views

Finding text files in a given path and applying a function to those files

I made a function called "SolveLinearSystem[]" that solves,as its name suggests, a linear system of any amount of variables. It takes the path of a text file as its only argument. The function then ...
0
votes
0answers
58 views

Normal ordering in Mathematica

I want to create a function which normally orders a string of field operators. Consider the following: $$\langle0\vert\hat{a}(k_n) \cdots \hat{a}(k_2)\hat{a}(k_1)\hat{a}^\dagger(k_1)\hat{a}^\dagger(...
0
votes
0answers
55 views

Problems with Tooltip

I an getting strange behavior with functions built using Tooltip. I create a function to display the position of data in a list ...