Questions tagged [sow-reap]
The sow-reap tag has no usage guidance.
42
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Optimization of conditions applying
Let we have some data generator, e.g. lazy tuples or permutations.
I need to select data by some conditions cond1, cond2, …, up to 5-6 conditions.
All of them need ...
- 1,085
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votes
2
answers
207
views
Recreating Poincaré section for a double pendulum
I am trying to recreate the Poincaré Sections for the double pendulum as described in this paper. I am unable to figure out a way to include energy values in the code. The code that I used until now ...
- 899
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3
answers
96
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How do I create a Table from a For loop?
I've been trying to create a table that has the % of the cycle of a sample and the module of acceleration for the first 100 values, but I don't know how to create it. Here's the code:
I have imported ...
- 1
5
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2
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223
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Join not working
I am trying to append elements to a list in Mathematica using the join function but it is not working. Here is a small working example:
...
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1
answer
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What Reap/Sow tricks do you use?
I admit that I have been reluctant to use Reap and Sow for years and that I used it only when I had no choice with ...
- 5,637
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Using Reap Sow to define unsorted union [closed]
In the documentation of Reap under "Applications" paragraph there is this example:
...
- 7,044
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38
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What is the best memory utilization and efficiency considerations for simulating particles that are randomly created and removed?
I am wanting to run a simulation involving a varying number of "particles" (points defined by 2D coordinates $(x,y)$ within some region). At each time step, there is a probability that a new ...
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Keep Reap / Sow results after breaking out of a loop [closed]
I am doing a long calculation where I create a list using Reap and Sow. However, sometimes this calculation gets too wild and I ...
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2
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What happens if you don't Reap what you've Sown?
As I understand it, when using Sow[expr] you throw the expr on some private stack which you can ...
- 1,460
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1
answer
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Bifurcation diagram for Lorenz attractor
As I was following a similar question I came across a beautiful answer here. However, in that code, he used InternalBag[] which heavily depends on ram that I can't ...
- 1,492
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Sowing Once into Each of Many Lists – Any Better than Append?
In general
I know to try to use Reap and Sow over Append or AppendTo due to superior performance. However, Reap and Sow are notorious for being difficult to understand how to use and how they work ...
- 1,597
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39
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Sow and Reap returning different results for the same expression [closed]
Consider the following trivial example:
...
- 5,097
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How do the functions Reap and Sow actually work behind the scenes?
I have read that using Reap and Sow to generate a list of unknown length is much more efficient than using AppendTo over and over. I believe AppendTo works by creating a new list that is one element ...
- 344
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Can I parallelize this function?
Can I and should I parallelize this function ? my aim is to have faster calculations
below is a toy function in which I kept the structure of the real function I am using. It uses ...
- 964
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67
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Getting columns (instead of rows) using Reap/Sow
In my program, I'm computing a vector inside a Do loop. The example below is an overly-simplified version, but the structure is the same (the original code can't be ...
- 37
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Problems with NDSolve and initial conditions (NDSolve::nbnum1:)
this is the situation, I'm trying to solve a system (s1) with two differential equations, called "x[Ne]" and "y[Ne]". They have and initial condition that first need to satisfy ...
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356
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How to pick consecutive numbers from list?
Question is very simple.
If we have
tst = {2,3,4,6,7,9,11}
result must be
{{2,3,4}, {6,7}, {9}, {11}}
There are similar ...
- 1,085
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Why Reap and Sow is not working here [closed]
Here in the first example my code works:
Reap[
For[x = 1, x <= 10, x++,
f[x];
Sow[{x, f[x]}]]][[2, 1]]`
and I can plot $x$ vs $f(x)$.
However, ...
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Accessing sowed data during long computation
This question is very similar to the one posted here: Interrogating a running evaluation but my running computation consists of a backtracking procedure which sows valid solutions. It is hard to tell ...
- 1,460
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What is the meaning of [ ][[ ]]? [duplicate]
I have a question about these two pieces of code
Reap[
For[i = 1, i < 10, i++, Sow[i]; Sow[i^2]; Sow[i!]; Sow[N@Log@i]];
][[2, 1]] ~ Partition ~ 4
and
<...
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3
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How to Sow[] until I've Reap[]'d enough?
I have a process that returns an unpredictable number of data points, and I'd like to run it repeatedly until I have a certain number of points.
My actual code is too complicated to use an ...
- 4,481
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2
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126
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How to assign output of `Last@Reap` to a variable? [closed]
I would like to define a variable that equals the solution of a numerical equation. Usually something like smax=zmax/.FindRoot[Exp[-zmax/2]==2,{zmax,0}] would work. ...
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152
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I need an alternative to AppendTo using Reap and Sow
c = Table[RandomVariate[BernoulliDistribution[1/2], 3], 3]
d = Total[c, {2}]
list = {};
For[k = 0, k <= Length[d], k++,
If[d[[k]] == 2, AppendTo[list, c[[k]]]]]
...
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160
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Reap and sow for BreadthFirstSearch
The following Code highlights the breadth-first scan tree
...
- 1,596
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124
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How to control which list Sow puts elements in
I'm trying to Reap/Sow elements of a list into separate sub-lists. In this toy example, I want evens in one list, odds in the other. But whichever sub-list d[[1]] happened to belong in, that sub-...
- 4,481
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211
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Reap and Sow Tags. How to retrieve part of list belonging to specific tag? [closed]
I'm trying to improve my code's performance by using reap and sow instead of appendto and it works, but I hit a small obstacle. Since my code is building two lists simultaneously, I need to use sow ...
- 155
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1
answer
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How to use Reap and Sow instead of Append to
I have matrix and and i want to do increment in a do loop and and i want to store in list using append to. It works fine for less values, But when i want to do it for values around 1 million the ...
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1
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Understanding Sow and Reap documentation
Both in Sow and in Reap documentation there is the example:
...
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WhenEvent, Storing Sow data, Loops
My problem is essentially to do with manipulating and storing Sow data in a nested loop structure.
I have a set of differential equations describing time-evolution of a bunch of variables. ...
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566
views
Better definitions of Reap and Sow
I am having tremendous difficulty understanding Reap and Sow in Mathematica. The definitions are pretty circular. When I look at the definition of Sow, I get, "specifies that e should be collected by ...
user54649
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112
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Poor performance from Manipulate and Sow-Reap
I am not a mathematician, and I barely know how to use Mathematica. But, over the course of many months and with help from this site awhile back, I managed to generate dynamic output that does exactly ...
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Sow in WhenEvent can't extract parameter value of ParametricNDSolve
This is a problem I noticed when trying to answer this question. Just consider the following toy example:
...
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How to keep building list until manually stopped?
I would like to run a numerical experiment for as much as it can run in a reasonable time.
This is a sketch of how I currently do it:
...
- 325
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1
answer
198
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Timing functions with Sow / Reap and AbsoluteTiming
I have a main function f[x] that calls three sub-functions:
...
- 1,631
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Reap unpacks packed arrays
I noticed that Reap unpacks packed arrays. I've looked at previous answers but am still an unsure whether this a serious issue.
E.g. consider Ex 47.3 from EIWL:
...
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792
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Writing Faster Mathematica Code - Sow and Reap?
I am applying Select function to a large list called xyCoordinateCentreCircle.
The dimensions of the list are:
...
- 617
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Why is Reap result nested? [closed]
A minimal (toy) example for my question:
i= 1;
Reap[Do[Sow[i = (i + 1)^2], {4}]]
(* {Null, {{4, 25, 676, 458329}}} *)
I presume the entire result is a ...
- 11.7k
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Reap, Sow with Parallelize: bad performance, why?
I have a question about the performance of Reap and Sow with Parallelize. I am aware of the following questions
How to collect result continuously (interruptible calculation) when running parallel ...
- 5,423
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1
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162
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Is Sow/Reap compatible with Composition?
I'm trying to figure out why these two pieces of code return different results. As expected,
f[Reap[Sow[x]]]
gives ...
- 1,783
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votes
1
answer
390
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Elements in `Reap` and `Sow`
Can someone help explain it to me:
How does here e come out? Why b disappears?
...
- 517
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votes
1
answer
700
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Defining Tags in Reap
I am trying to use Sow/Reap to replace Append in my code. The problem is that I need to ...
- 133