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.
0
votes
1answer
23 views
Have the kernel load a user-defined function by default
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 ...
17
votes
3answers
244 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
0answers
45 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):
...
1
vote
0answers
34 views
Unexpected error message from GraphPlot evaluation [closed]
(Running MMA 9 on Mac OSX 10.8.3, MacBook Pro, 16GB RAM)
I am trying to display a graph with GraphPlot. I want a few of the edges to be purple, and the rest red. I figured out a way to do this that I ...
0
votes
0answers
11 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
97 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 ...
10
votes
1answer
153 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 ...
1
vote
2answers
141 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 ...
24
votes
2answers
409 views
Variable naming changes everything
I am having a rather unusual problem I do not understand with Mathematica where renaming one of the variables of my function causes the function to stop "working". Here is the example of the code ...
11
votes
2answers
241 views
Using several anonymous functions mixed together
This works:
list // BarChart[#[[2]], ChartLabels -> DateString @@@ #[[1]], ChartStyle -> "Pastel"] &
This doesn't:
...
3
votes
2answers
79 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
66 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
89 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
131 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 ...
1
vote
2answers
400 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 ...
1
vote
1answer
78 views
Mathematica plots a discontinuity in piecewise function that does not exist [duplicate]
I have the following function defined:
...
2
votes
3answers
98 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
268 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
228 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
74 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
148 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
0answers
64 views
How can I get tabular output for the results of my simulation? [closed]
I have code that simulates a simple Markov Chain and looks like this:
...
3
votes
1answer
58 views
User-defined NormFunction in FindFit -
I would like to use a different Norm instead of a p-Norm in FindFit (Mathematica 9). For example, instead of using
Sqrt[Sum[(x_model - x_data)^2]]
I'd like to use
Sum[x_model/x_data].
I can ...
0
votes
2answers
134 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
65 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
67 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, ...
9
votes
3answers
128 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 ...
3
votes
1answer
159 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
199 views
11
votes
1answer
127 views
How can I make threading more flexible?
Threading automatically with Listable functions requires the argument expressions to have the same length (or for one of them to be atomic). For nested lists the ...
21
votes
1answer
271 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 ...
27
votes
9answers
6k 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
267 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
14
votes
5answers
766 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
55 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
201 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
74 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
...
0
votes
1answer
268 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 ...
0
votes
0answers
44 views
Finding coefficients that make certain functional expression vanishing
My problem is to find a procedure that gives coefficients which make certain functional expression vanishing.
For example if I have a polynomial $P(x)$ of one variable $x$ given by $P(x)=a_0+a_1 ...
5
votes
2answers
243 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
76 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
152 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 ...
8
votes
4answers
135 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
195 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
93 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
465 views
Passing down arguments
In R, one can use ... to pass arguments down to another function. For example
...
-1
votes
1answer
66 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:
...
10
votes
3answers
388 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
106 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 ...
6
votes
1answer
63 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 ...
