Linked Questions

0
votes
1answer
4k views

Loops and subroutines [duplicate]

Possible Duplicate: Alternatives to procedural loops and iterating over lists in Mathematica I am new to Mathematica and not familiar with functional programming. In particular, I have no idea on ...
0
votes
2answers
553 views

Seeking faster method than using Table and If together [duplicate]

See the example below. Is there any way to make this execute much faster and still get the same output ? I have read Conditionals slower than operators? but it didn't really help me as I can't seem to ...
1
vote
1answer
572 views

For loops in Mathematica [duplicate]

I'm actually the first time using loops in Mathematica. For example, I have: For[i = 1, i <= n, i++, For[j = 1, j <= n, j++, ....] How it is possible now ...
1
vote
1answer
247 views

How should I go about writing more functional and list based code? [duplicate]

I've heard that Mathematica is usually faster when the code is list-based and/or uses a functional paradigm. I'm still working on getting the hang of this; there are a lot of ...
6
votes
0answers
153 views

What are some general strategies to avoid using For loops? [duplicate]

Possible Duplicate: Iterating over lists in Mathematica While there are some cases where a For loop might be reasonable, it's a general mantra – one I ...
2
votes
0answers
116 views

Want explanation of when different looping constructs are appropriate [duplicate]

For example when would you use a Do loop over a For loop? For which tasks would you use Map, ...
0
votes
0answers
54 views

What techniques have you employed to avoid loop in Mathematica? [duplicate]

It appears to me that loop in mathematica is very slow (compared with matlab). Since many people still use mathematica to finish their work, there must be some techniques to bypass this problem. ...
457
votes
37answers
102k views

What are the most common pitfalls awaiting new users?

As you may already know, Mathematica is a wonderful piece of software. However, it has a few characteristics that tend to confuse new (and sometimes not-so-new) users. That can be clearly seen from ...
535
votes
19answers
135k views

Where can I find examples of good Mathematica programming practice?

I consider myself a pretty good Mathematica programmer, but I'm always looking out for ways to either improve my way of doing things in Mathematica, or to see if there's something nifty that I haven't ...
39
votes
12answers
3k views

Map a function across a list conditionally

It seems that this is a really basic question, and I feel that the answer should be obvious to me. However, I am not seeing. Can you please help me? Thanks. Suppose I have a list of data ...
84
votes
3answers
13k views

Why should I avoid the For loop in Mathematica?

Some people advise against the use of For loops in Mathematica. Why? Should I heed this advice? What is wrong with For? What ...
57
votes
5answers
6k views

Are there any cases when For[] loops are reasonable?

To my mind the only reason for the existence of For[] loops in Mathematica is to allow new users with some experience in procedural programming languages to write ...
17
votes
7answers
4k views

How do I check if any element in a list is positive?

As a simple example of what I would like to do, suppose I have a list a of all real numbers. I would like to perform a simple check to see if some element of ...
49
votes
2answers
6k views

Scan vs. Map vs. Apply

I cannot understand the difference between Apply, Scan, and Map. I have tried to play with ...
8
votes
8answers
2k views

Finding the midpoints of an ordered list of numbers

Suppose that I have an ordered list of numbers. The numbers in the list may be evenly spaced, but they may not be. Here are two examples, list1 and ...
11
votes
4answers
10k views

Removing all values from a list that satisfy a given condition

Suppose I have a list, list = Table[{n}, {n, 1, 5}] (* list = {{1},{2},{3},{4},{5}} *) and I want to remove all values from this list that are greater than 3, so ...
19
votes
2answers
957 views

Shorthand for map at level 2

I love the shorthand /@. It is amazing for readability (and laziness when typing). However, right now I find that I need Map at level 2, i.e. ...
7
votes
2answers
9k views

Creating custom functions with multiple arguments

I am hoping that this isn't a stupid question so feel free to vote it for closure. Google failed somehow. I want to define a custom function (more complicated than the usual ...
9
votes
4answers
3k views

Implementing Picard's Iteration for solving ODEs

Picard's Iteration is a way of solving the IVP $$y'(x)=f(x,y(x)), \quad y(x_0)=y_0 $$ It consists of defining the following sequence of functions recursively: $$y_0(x):=y_0 \\ y_{n}(x):=y_0+\int_{...
2
votes
6answers
3k views

Selecting elements from a list one by one

I have an list: l = {{4,5},{7,8},{9,5},{3,2},{1,2},{13,12}}. I want to take the elements in the list in the sequential order. For example the first element in ...
13
votes
4answers
495 views

The gap between MapAt and ReplacePart for 2D data tables with headers

Consider a relational table derived from survey data, where each column ("001-01" ...) represents a responder and each row (...
7
votes
5answers
906 views

What is primary, function computation or function application?

What is the order of computations here? g[x_]:=x^2; f[x_]:=Sqrt[g[x]]; Map[f, Range[100]] Does this code first gets $f(x)=x$ and then gives its values or for ...
11
votes
5answers
1k views

Relational joining of tables

A common thing to want to do with data is to combine it (at least I thought this was a common thing). In SQL there is the idea of table joins "select id,v1,v2 from A,B where A.id=B.id" kind of thing. ...
5
votes
3answers
303 views

First evaluation fails

I am fairly new to Mathematica (version 7), so please bear with me... I have duplicated, in Mathematica, a program that I originally wrote in C (it generates OEIS sequence A191837). The problem is ...
1
vote
3answers
6k views

Loop through a list and select elements

I am new to Mathematica and I have no idea how to make a basic for loop work. I want to loop through the elements of a list: Range[45, 200]. I want to select the ...
8
votes
3answers
689 views

Rewriting For loop to FoldList or similar

In CrossValidated, the answer to a question on prediction of number of viewers of Gangnam Style is given in R. I have mapped the answer directly to Mathematica: ...
5
votes
3answers
860 views

Is Table the only functional way to construct nested loops in Mathematica?

Suppose you have a cubic box containing identical particles and you want to compute the distances between each particle and every other particle in the box without double-counting (i.e., if you've ...
0
votes
3answers
1k views

In nested For-loops, I want the second For-loop to be evaluated only once in each cyle

I want to print A[0, 0, 1], A[0, 0, 2], A[1, 1, 1], A[1, 1, 2], A[2, 2, 1], A[2, 2, 2] using the following code. ...
2
votes
4answers
4k views

How to export data from For loop in text file?

I'm new in Mathematica and I am trying to write numbers from 1 to 10 in txt file. But "Null" is everything that is written in my file. The code is: ...
5
votes
3answers
1k views

How to speed up a process

I am wondering how to speed up the following code: Currently it takes more than two sec to be processed. ...
0
votes
3answers
4k views

How do I show the combined plot from the do-loop?

I have a do-loop to do the calculations from a set of data and plot the graphs with different results, that was obtained from the calculations. I was able to get multiple graphs but I want to ListPlot ...
2
votes
1answer
3k views

converting Matlab program to Mathematica code

I have the following Matlab program; ...
5
votes
4answers
4k views

Finding the area of a circle using monte carlo simulation [duplicate]

I wrote the following code to find the area of the circle $x^2+y^2=1$ using monte carlo simulation : ...
3
votes
3answers
1k views

For-loop not working as I expect

I want to do this: When 10 <= t < 130, give t -> 1; When 130 <= t<300, give <...
2
votes
5answers
2k views

Assigning a particular value to array elements

I have an array of 10000 elements. I want to randomly assign energy to these 10000 elements using Gaussian or Exponential distribution, such that each time a particular element is selected its energy ...
5
votes
3answers
480 views

What is the right way to write a function that includes other functions?

I want to include multiple sub functions: $b(x) = 10x$ $w(x) = s + b(x)$ $c(x) = x^2$ into two main functions: $ua(x) = w(x)-c(x)$ $ub(x) = w(x)-c(x)^2$ As a reaction to this answer, I wrote ...
4
votes
4answers
255 views

How to avoid writing $K$ loops?

I want to evaluate a mathematical function of $K$ variables each of variables varying between 1:N. One way to do this is writing $K$ loops and varying variables accordingly, as shown below: ...
6
votes
2answers
165 views

Achieve performance that is competitive with numpy [duplicate]

What are the best practices to ameliorate time performance of Mathematica? As a practical example how we can decrease timing below? ...
7
votes
2answers
479 views

CUDA image processing

I am having an issue with image processing involving CUDALink. ...
3
votes
3answers
2k views

Draw grid lines at multiples of k

Here is a beginner's question: when creating plots with mathematica, I want the grid lines to be at multiples of a constant value. E.g. in the following plot, the vertical grid lines are at multiple ...
4
votes
3answers
393 views

Alternative forms to Table for iterating over replacement rules

I have a multivariate polynomial x. I get coefficients of various monomials using CoefficientRules, which returns a list of ...
0
votes
1answer
7k views

How do I store values in a for loop into an array and then plot that array? [duplicate]

What my title said and I want to plot the values of the array. still new to mathematica and programming so its hard to formulate my question just right
3
votes
1answer
907 views

3 hour calculation? ParallelMap & ParallelTable

I'm having some problems with slow Mathematica code... I'm basically doing a computation that's is expected to take 3 hours (!) in my Core i7 with 4 processors... I'm basically computing an index (of ...
4
votes
3answers
1k views

Stop Computation - Is Exit[] overkill?

The following example either finds a factor of the number $n$ or returns a message saying that the number in question is prime (I specifially wrote this to demonstrate my question below). ...
4
votes
2answers
395 views

Can't use my own discontinuous coefficient within NDSolve

I want to evaluate the pendulum's motion with changing equilibrium state given by eqilValue[t]: ...
4
votes
2answers
227 views

Confusing ReplaceRepeated & Hold

I've been bootstrapping myself to the very alien world of Mathematica and there came my first WTF moment: ...
6
votes
3answers
451 views

How to populate a large sparse array efficiently

I am trying to populate a large 2D sparse array and sum up all the columns at the end. I tried generating a set of rules and then generate a matrix using SparseArray or break the data into chunks but ...
4
votes
3answers
271 views

Declaring lists

Do I have to declare a list before using it in a loop? for example: For[i = 1, i < 10, i++, A[[i]] = i]; The output is: ...
5
votes
3answers
325 views

Question about Map and Total

Suppose I have a list and I want to generate a new list, such that $$ NewList[index] = \sum_{index \neq j}^{NumOfElts} \frac {1}{ \lvert OldList[index]-OldList[j] \rvert ^2 } $$ Can I do it using ...
1
vote
2answers
3k views

Tag List is Protected Error in simple script

I want to have a simple script that gives me all numbers $k \in \mathbb{N}$ in some range such that product of all their divisors is equal to $k^3$. Here is the code that I wrote: ...

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