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Questions on the manipulation of List objects in Mathematica, and the functions used for these manipulations.
0
votes
ListLogPlot for positive and negative values
This could be made nicer, but how about something like this?
GraphicsColumn[{
ListLogPlot[Select[xp, #[[2]] > 0 &], PlotRange -> {{0, 10}, All},
PlotRangePadding -> Scaled[.05]],
ListLogPlot[A …
9
votes
Sensitivity analysis of parameter on eigenvalues of predator-prey model
Here's a solution using my EcoEvo package, which is designed for just this kind of problem. First, install the package (only need to do this once):
PacletInstall["EcoEvo", "Site" -> "http://raw.githu …
2
votes
Accepted
ParametricNDSolve with a delay differential equation
I think the easiest way to get what you want is with Table:
z0 = 1; ta = 0.01;
ytotal[ta] = Table[z0 = y[z0, ta][T] /. sol, {i, 100}];
For those parameter values, it looks like the population quick …
5
votes
Accepted
Using Manipulate to plot a function's time evolution
Not sure you know this, but if you use Plot you don't need to manually define the x-coordinates.
Plot[Evaluate[Table[f[x, t], {t, 0, 0.9, 0.1}]], {x, -1, 1}]
The Evaluate is only necessary to get …
8
votes
Converting a backward/forward sweep code for optimal control to _Mathematica_
According to chapter 9, "Mathematica’s NDSolve can take in boundary conditions, and system (9.26) can be directly input into it" (p. 239). Let's give it a try.
β = 0.05; μ = 0.01; γ = 0.5; n = 100; …
4
votes
I wanna get a result of i/j . Like 1/3, 1/5, 1/7, 3/5, 3, 5/3... Something like that. But no...
How's this?
range = {1, 3, 5, 7, 9};
DeleteCases[Flatten[Table[i/j, {i, range}, {j, range}]], 1]
(* {1/3, 1/5, 1/7, 1/9, 3, 3/5, 3/7, 1/3, 5, 5/3, 5/7, 5/9,
7, 7/3, 7/5, 7/9, 9, 3, 9/5, 9/7} *)
6
votes
4
answers
712
views
MaxDetect speed
What's the fastest way to find the local maxima of a 2D list? E.g.
nx = ny = 100;
dat = Table[Sin[2. \[Pi] x/nx] (0.1 + Cos[2. \[Pi] y/ny]), {y, 0, ny}, {x, 0, nx}];
ListPlot3D[dat]
This (updat …
17
votes
Accepted
Can't make more than 249 Internal`Bags in a Table
Seems to be the same underlying issue as here: by default, Table compiles its argument when the number of values is 250 or more. Evidently Internal`Bag doesn't like this!
If all Internal`Bags are th …
13
votes
1
answer
197
views
Can't make more than 249 Internal`Bags in a Table
I need a lot of Internal`Bags so I made them with Table. It works fine for 249 or fewer Bags but goes horribly wrong for 250 or more:
Table[Internal`Bag[0], {i, 249}]
(* {Internal`Bag["<" 1 ">"], .. …
1
vote
Incorrect results from simple `Plot`?
Another solution: increase the PlotPoints in testPlot2:
testPlot1 = Plot[Log[HarmonicNumber[n]], {n, 1, 5}];
testPlot2 =
Plot[Log[HarmonicNumber[n]], {n, 1, 43}, PlotPoints -> 100];
Show[testPlot1 …
7
votes
Accepted
Using lists for creating a bifurcation diagram of an iterative map
Here's one way, using Replace to wrap your points x with {r,x} and Table to iterate over r.
res = Flatten[Table[
list = RecurrenceTable[{x[n] == r (x[n - 1] - x[n - 1]^3), x[1] == 0.5}, x, {n, 1, 2 …
1
vote
0
answers
70
views
Problem using ConstantArray in FindRoot
I ran into a strange problem, where using ConstantArray inside FindRoot results in a FindRoot::jsing error. Here's a minimal example, with the first instance working and the second failing:
FindRoot …
1
vote
Accepted
Table with the logarithmic step
Something like this?
f[x_] := x^2;
With[{x := 10^xp}, Table[{x, f[x]}, {xp, 0, 5}]]
{{1, 1}, {10, 100}, {100, 10000}, {1000, 1000000}, {10000, 100000000}, {100000, 10000000000}}
7
votes
Plotting the number of fixed points of a system of two nonlinear differential equations
For this particular example you can find the bifurcations analytically by also setting the slopes of the isoclines to be equal.
eq1 := x^2 + y + b;
eq2 := x + y^2 - a;
bif = Solve[{eq1 == 0, eq2 == 0 …
1
vote
List positions without brackets
I think Sequence does the job for you:
a[[Sequence @@ l[[1]]]]
(* a11 *)
Equivalently, without (most) brackets, call it Part:
Part[a, Sequence @@ l[[1]]]
(* a11 *)