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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6
votes
0answers
105 views

Is there a function to generate a minimal clique cover?

This is a graph problem known as the "Clique Edge Cover" or "Intersection Number" problem, and the goal is to find, from a given graph like $E=\{\{a,b\},\{a,c\},\{b,c\},\{b,d\},\{c,d\}\}$ and ...
2
votes
3answers
366 views

Generating pairs of additive and multiplicative factors for integers

Given an integer $n$, I want to get two lists: a) the set of pairs of the divsors $a,b$ into exactly two factors $n=a\cdot b$, b) the set of pairs $a,b$ of two summands $n=a+b$. The code I ...
7
votes
2answers
128 views

Change some option of a function when calling it [duplicate]

Say I have defined some function like f[p_] := Plot[Sin[p*x], {x, 0, 2 Pi}] Now in most cases, I just need to specify the value of ...
-1
votes
1answer
191 views

How to define a pure function with a Module?

I was not able to use a self defined (using Module and For loops) piecewise function to fit data. It seems that the problem is that I have to define a pure function. I would like to learn how to ...
8
votes
2answers
141 views

Possible to scope an anonymous function within Module?

This is my first question. I'm fairly new to Mathematica and completely new to SE, so I apologize if this question is trivial. I'm working on a problem that requires a function to be redefined ...
1
vote
0answers
45 views

Using anonymous functions instead of module or block. Bad idea? [duplicate]

Here is an example function which returns True if a point p is on an (open) line segment (A, B) assuming that Orientation[A, p, B] returns 0 if the three points are collinear: ...
3
votes
2answers
92 views

How to apply multiple/complicated requirements for a pattern in a function input [duplicate]

In this question. I suggested that to test whether the input of a function was a matrix of numbers one could create the following test: ...
21
votes
4answers
619 views

Why is there no PositionFunction in Mathematica?

Too often I have seen the programs of inexperienced users greatly slowed by using Position in an iterative fashion, when far faster would have been to compute a ...
0
votes
1answer
54 views

Have the kernel load a user-defined function by default [duplicate]

I wrote a very simple function that I would like to act as if it were one of the default functions that came with Mathematica, so that you don't have to load or import any package before you make use ...
0
votes
0answers
53 views

Question regarding function definition overloading / argument passing test [duplicate]

It is possible to define function dependently to passed argument type or condition this argument fulfills (somewhat like overloading): ...
0
votes
0answers
23 views

How to assign values to a function at discrete points? [duplicate]

Suppose we are interested in a function f[x] that is defined only at discrete points: x = {1.1, 2.1, 3.1, 4.1, 5.1} We want to ...
5
votes
3answers
196 views

Applying a function with the HoldAll attribute inside NestList

I'm trying to write an update function, which can be applied to a list and then to NestList it. As the function has to manipulate the given variable I figured I ...
11
votes
1answer
255 views

Modules that initialize themselves on first call

I use a lot of functions that extract a specific data item from a file with many data items. I want these functions to load data (slow) and return the item (fast) on first call, but just return the ...
2
votes
2answers
280 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 ...
14
votes
2answers
340 views

Using several anonymous functions mixed together

This works: list // BarChart[#[[2]], ChartLabels -> DateString @@@ #[[1]], ChartStyle -> "Pastel"] & This doesn't: ...
4
votes
2answers
580 views

How to define a polynomial/function from an array of coefficients?

I have the coefficients of my desired polynomial in an array CoefArr (I'm new to mathematica, so I think of everything as arrays, it is actually a list I believe) starting with the constant at index ...
2
votes
2answers
97 views

Putting a matrix inside function

I want to fit a function to some data and inside the function there's a list here's my data ...
-1
votes
2answers
306 views

How can I define a function which is the sum of other functions?

I have a function which is summation of another function over different i,j iterators. U[r] = Sum[V[r, i, j], {i, 1, 5}, {j, 6, 10}] and ...
4
votes
3answers
162 views

How can I combine two Pick expressions into one?

I want to speed up my code, i.e., replace Select by Pick. I think using two Pick ...
5
votes
2answers
1k views

How to define a differential operator?

I have a linear differential operator, for instance, $L\left (\partial _{t} \right )=\partial _{tt} - 3\partial _{t} + 2$. I use it in 2 different ways: apply the operator to a function: $L\left ...
2
votes
3answers
136 views

Map several functions in one routine

I have several functions, let's assume they are: func1[x_]=x; func2[x_]=3*x-5; func3[x_]=0.1*x^2; and a lot more like these. For each and every one of these I ...
7
votes
4answers
423 views

How can I shorten this code to rotate a line segment around its center?

I have a list of line segments stored in the form: { {{x11,y11},{x12,y12}} , {{x21,y21},{x22,y22}} , ... , {{xn1,yn1},{xn2,yn2}} } Now I want to rotate all of ...
5
votes
4answers
366 views

Any rule of thumb for converting a simple mathematical expression into a pure function?

By simple mathematical expression I mean one with a few functions and few variables copied into MMA in a mechanical way from a math book. For example this one, giving the distance between two points ...
0
votes
1answer
100 views

Strange function definition result [duplicate]

I'm relatively new to Mathematica, and I'm trying to define a function f(k) that would do the following: For any positive integer $k$, a finite sequence $a_i$ of fractions $\frac{x_i}{y_i}$ is ...
0
votes
2answers
511 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 ...
0
votes
2answers
383 views

Fast Autocorrelation Computation

I want to compute the Autocorrelation Function (ACF) of a data table with $10^6$ entries. I know that there is a built-in function in Mathematica for that, but because I do not know how exactly it is ...
0
votes
1answer
90 views

Function giving negative value when it should be positive [closed]

I am trying to evaluate $$\displaystyle J=A\sum_{k=0}^{n-2}(-1)^k{n-2 \choose k}B^{n-2-k}\left(\frac{C_1}{k+n}-\frac{C_2}{k+n+1}+\frac{C_3}{k+n+2}-\frac{2}{k+n+3}\right)$$ in Mathematica as a function ...
2
votes
2answers
94 views

Rising Recursion Relationships

Lets say I want to compute the following function in mathematica: $G[n,k]=G[n+1,k-1] + G[n+2,k-2]$ where I know that $G[n,0]=n$ and $G[n,1]=n^2$. So, for example, $G[3,2]=G[4,1]+G[5,0]=4^2+5$ or, ...
11
votes
3answers
254 views

Pass by reference for an option argument

Pass by reference can be faked by using HoldAll or something similar in the definition of a "Function". But can pass by reference be faked for symbols passed as ...
5
votes
1answer
477 views

Stereographic Projection

Say I want to represent points of the complex plane in the sphere $\Bbb S^2$ using stereographic projection. That is, the Riemann sphere: Specifically, it would be nice to be able to: Given the ...
6
votes
3answers
333 views
24
votes
1answer
370 views

which is better, using Assert[] or manual checks on arguments and other computations?

I never used Asserts in Mathematica, but trying to see what advantage they have over just argument check and additional definitions of the function to capture unwanted input. For example, which one ...
32
votes
9answers
7k views

Generating a Sierpinski carpet

I am trying to draw a Sierpinski_carpet. I have code that works, but I think there is a more elegant way to do than my way. Maybe I couls use Tuples or ...
6
votes
1answer
297 views

How can I define a function that can accumulate its parameter?

For example, write a function add: add[3] return 3 add[4] return 7 add[10] return 17
16
votes
5answers
1k views

The difference between 0. and 0

I have a function for which 0 is a special case: f[A___, 0, B___] := 0 But since I am doing numerics, sometimes in the course ...
1
vote
1answer
84 views

NMaxmize with a list of variables

I want to use NMaximize to find the maximum value of a function with multiple variables. The problem is I would like to set this up so the number of variables is only decided when the function sees ...
6
votes
3answers
283 views

Using function with multiple definitions in Manipulate

I'm trying to use Manipulate to visually try out different values of lambda in a Box-Cox transformation. I've created a boxcox ...
4
votes
2answers
84 views

Creating functions from output of other calculations

Apologies in advance if the title is vague, I'm not really sure what to call this. I have a function (call it 'foo') that generates a largeish polynomial, and it is natural to make the variables be ...
-1
votes
1answer
742 views

How can I make a plot of the Higgs potential?

I was wondering, how would could I make a drawing of the Higgs potential aka "mexican hat potential". I am quite new to Mathematica and don't know where to look to learn how to implement such a ...
4
votes
2answers
1k views

Gram Schmidt Process for Polynomials

I want to implement the Gram Schimdt procedure to the vector space of polynomials of degree up to 5, i.e. I want to find an orthogonal basis from the set of vectors $v=(1,x,x^2,x^3,x^4,x^5)$. The ...
0
votes
1answer
81 views

Given a sequence of expressions, how can I convert them all into functions?

I have a sequence of expressions 1, x, x^2, ..., x^5 I want to define a sequence of functions out of it, what should I do? Namely I want to define a vector of ...
9
votes
2answers
235 views

How can I get the right hand side of a delayed expression?

Imagine there is a given function f, defined with SetDelayed, say f[x_] := Sin[x]^2 + Cos[x]^2. Is it possible to get rhs of ...
9
votes
4answers
245 views

How to pass a list of arguments into HoldAll

I have a list of arguments (which in reality is lengthy): arguments = {a, b, c} arguments2 = {a_, b_, c_} f[Sequence@@arguments2] := a + b + c Note: It seems ...
0
votes
1answer
618 views

How can I define a Step-Wise function in Mathematica (Not using Heaviside Step Function)? [closed]

I need to define a function, which has very different behaviour in different regions. There are about 13 different regions. A sample of my function is the foloowing table: I want to define it as a ...
4
votes
2answers
147 views

How to only work on sublists with non-zero (or positive) values

i have a large compositional dataset which contains non-zero and zero values. here is a sample: ...
10
votes
3answers
681 views

Passing down arguments

In R, one can use ... to pass arguments down to another function. For example ...
-1
votes
1answer
109 views

Dynamically show a specific number of the fractional part's digits

What is the fastest way to cut off all n z digits of the fractional part of a real number? (For example 12390.20934230) I came up with this so far: ...
11
votes
3answers
853 views

What is Mathematica's equivalent to MATLAB's filter function?

The MATLAB code filter(0.5,[1, -0.5], [1:10]) is equivalent to Rest@FoldList[(#1 + #2)/2. &, 0, Range[10]] I don't ...
2
votes
3answers
187 views

Defining a function to determine when convergence is guaranteed

I'm investigating how many iterations are needed for a particular orbit to reach a fixed point of a function. Since I have many functions to test, I want to define a function in Mathematica that will ...