Questions about how Mathematica evaluates expressions, tracing evaluation (Trace*), handling expressions in unevaluated form (Hold*, Unevaluated), nonstandard evaluation, etc.

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1
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5answers
174 views

Do not expand matrices in Mathematica calculation

Here is an example of a problem I'm having. Consider that I have defined: omega={{p[t]},{q[t]},{r[t]}} x={{a},{b},{c}} R={{1,2,3},{4,5,6},{7,8,d}} What I would ...
8
votes
4answers
301 views

How to inject unevaluated list of Unique into a RuleDelayed?

I am writing a function that constructs a rule which has Unique[] in the RHS. Here is a simplified segment of code ...
7
votes
2answers
151 views

Evaluation inside Inactivate

The documentation for Inactivate makes the function sound really powerful because it gives granular control over which kind of expressions specifically not to ...
0
votes
0answers
34 views

How to calculate a required definition only once for each iteration of NonlinearModelFit

This is my first post here. I've been using Mathematica for about 4 years now to analyze data, but am still very new and have no background in formal programming. This is the first question I couldn't ...
4
votes
2answers
78 views

Append fixed value to random selection of list

(This question might be an application of this other question, but there might be another solution specific to this application that I'm not aware of.) I am currently in a situation in which (in a <...
3
votes
4answers
102 views

Working with ScheduledTasks inside DynamicModules

I have a question - is it possible to run ScheduleTask[] inside DynamicModule[]? What I have tried so far: ...
3
votes
2answers
54 views

How to avoid 0 OverVector[F] to be evaluated as 0?

I am fairly new in Mathematica and I am trying to work with scalars and vectors. I decided to denote vectors using OverVector (as example, ...
7
votes
1answer
414 views

Debugging a $RecursionLimit error?

I sometimes encounter bugs that involve a recursion limit. It's often very hard to find the origin of the problem. Would there be a way to copy the stack somewhere and abort the evaluation in order ...
5
votes
2answers
132 views

A pre-parsed HoldForm

HoldForm holds an expression's parsed form not its actual "inputted form" e.g. ...
13
votes
5answers
256 views

Prevent Plus from threading

This is probably a very simple question, but I couldn't find a duplicate. As everybody knows, {x, y} + v gives {x + v, y + v}. ...
4
votes
2answers
101 views

Derivative before Numerical Integration

I need to take the derivative of a function that have a numerical integration on it. The variable in which the integration will be taken is not the same as the one in which the derivative will be ...
0
votes
1answer
297 views

How to force numeric evaluation?

I need to evaluate the PolyLog function at some points, but I'm interested in numeric values. E.g. PolyLog[3, 2.7] works fine, ...
1
vote
1answer
73 views

RunScheduledTask and return the result

I created a task that removes itself when an external variable x,is changed: ...
16
votes
2answers
911 views

How to restart computation when kernels die?

When an important process needs to be kept alive, there are monitoring tools to restart them if they die (e.g. god tasks in ruby), in my case I have an overnight scraping task that I need to have done ...
0
votes
1answer
52 views

Alter evaluation order when applying scalar multiplication to function

Consider the following program: g = 2f; g[x] (* (2f)[x] *) Is there any way I can change the above expression to have it return ...
3
votes
0answers
79 views

Is there an analogue of Evaluated->False (in FindRoot) for FindMinimum?

I guess functions like FindRoot, FindMinimum, etc puts the estimation number into the expression, and then do other calculations....
0
votes
2answers
45 views

Unevaluated derivatives of known functions after replacement

I want to make the following replacement work correctly: Array[(2 D[xM[[#1]][t], t] * D[xM[[#2]][t], t]) &, {3, 3}] /. {xM -> {Sin[ω t], Cos[ω t], 0}} ...
3
votes
1answer
102 views

Fast evaluation of a function in many points

I need to feed to an external program a number of points (in Complex128 format) generated from the numerical evaluation of some function, e.g. $e^{i \vec{k}\cdot\...
1
vote
1answer
232 views

new kernel for notebook

I know I can create a new kernel for my notebook from the evaluation menu but is there a command for this? I'd really like some of my notebooks to startup their own kernel as the first line of code.
4
votes
2answers
108 views

Manipulate in modal mode

It is sometimes convenient to use Manipulate to set up global values which are to be used in the rest of the notebook. In such cases one can select and run the ...
0
votes
0answers
54 views

What makes items with head `Function` different?

I apologize beforehand for the muddleheadedness of this question. It reflects the fact that I'm trying to interpret outward "behaviors" of Mathematica expressions without having any understanding of ...
0
votes
0answers
44 views

Order of evaluation for numeric functions

I'm trying to plot a 3D vector field to illustrate an electric field of a uniformly charged disk, and I used Manipulate to change the radius R of the disk to see ...
5
votes
5answers
220 views

Nested function with an increasing argument

If, for example, I have a nesting function like Nest[1 + x^n (#) &, 1, 3] it gives the result ...
3
votes
0answers
115 views

Assign variables from list inside With or Module

I have found that it is possible to assign variables from lists, as follows. r = {1, 2, 3}; {a, b, c} = r; b 2 However, ...
0
votes
1answer
122 views

Plotting two variables indirectly dependent on each other

I have the following system of linear ODEs for "i" number of species "c" migrating in "j" number of habitats: ...
19
votes
2answers
361 views

What does f_[whoCalled]^:=f really mean?

I came across the following post by John Doty in this Google Groups discussion: On Friday, January 11, 2013 8:23:16 PM UTC-7, amzoti wrote: It is clear the Mathematica uses Lisp as one ...
2
votes
0answers
52 views

Import names into notebook namespace [duplicate]

I have function that at some point has list of strings (e.g. {"apple","pear"}) and I want to declare (initialize) those variables in notebook namespace to default ...
1
vote
0answers
34 views

Save a Mathematica notebook evaluated [duplicate]

My notebooks can take some time to evaluate and by quitting Mathematica, I have to reevaluate every definition I've made once I restart Mathematica. Is there a way to tell Mathematica to save the ...
0
votes
0answers
86 views

Skipping sections of a notebook automatically

I have a notebook which allows to set some parameters at the start, and then does computations depending on these parameters. It is a long notebook and for readability it is broken up into sections ...
4
votes
1answer
52 views

How to adapt MSPToExpression function in $PrePrint?

I am introducing the mathematica Security (MSP module) to our system. The Document suggests use MSPToExpression as followed: ...
10
votes
1answer
122 views

Use EvaluationCompletionAction to notify me only after long evaluation

Is it possible to use the option EvaluationCompletionAction to notify me (e.g. with a Beep[]) when an evaluation that took ...
1
vote
1answer
49 views

Evaluation of InverseFunction at the boundaries of its domain

Folks, I want to numerically evaluate a InverseFunction h[x] close to the edges x5 and <...
8
votes
6answers
2k views
1
vote
1answer
39 views

Please explain this pattern/Message related issue and help with finding workaround

I attempted to clean up my code and also add messages to functions if they are called with wrong arguments. This introduced some error which I tracked down to the following: ...
10
votes
4answers
338 views

How to take and evaluate a specific part of a list without evaluating the rest?

I have a large list, for example, lis = {x + y, x y, Sin[x] y + Exp[y], x^2 y} and its elements depend on variables x and <...
2
votes
0answers
43 views

Executing selected code [duplicate]

In current Mathematica interface, if I select some piece of code and press CMD + Shift + Enter, the code is evaluated in place. Replacing the selected part by the evaluated version. The question is: ...
0
votes
0answers
73 views

Memoization and upvalues

Can I store an algorithm to one variable and the result as an upvalue to another? With regard to the problematic code below (real algorithm and argument test omitted), I would like to store the ...
1
vote
1answer
55 views

Creating a keyboard shortcut to change the Style of text [duplicate]

I'm editing a very long text in a Mathematica notebook and I'm using the "Article" stylesheet. In this text, code is highlighted using ...
6
votes
1answer
271 views

Dynamic and Refresh

If I am not mislead by my memory, in Mathematica 6 a function Refresh was introduced, having the options UpdateInterval and <...
1
vote
1answer
43 views

Showing updating message in Dynamic with UpdateInterval

I am creating an interface which needs to repeat an operation every few seconds. The operation itself is expensive but faster than the update interval of the interface. I would like to have some ...
11
votes
2answers
183 views

stop notebook evaluation when Assert fails

I would like a notebook evaluation to entirely stop when an Assert fails, without quitting the kernel. Is this possible (e.g., by setting ...
2
votes
2answers
89 views

PasteButton: Pasting expression name without quotation marks?

I am struggling to find a way to use PasteButton to paste the name of an expression (in particular a list) without showing the contents of the expression or without ...
2
votes
2answers
73 views

How can I use an InputField value as a variable name to save to?

I'm trying to save some settings and results from Manipulate, and I want to be able to save them to different variable names. The code I have is something like <...
22
votes
2answers
3k views

Difference between AbsoluteTiming and Timing

I need to evaluate the efficiency of my code. Therefore I would like to evaluate the time the code need for some calculations. Mathematica gives me two possibilities for this kind of evaluation: <...
23
votes
1answer
2k views

A one line proof that one is zero using Mathematica 10

a = (Sqrt[2] + 1) (Sqrt[2] - 1) - 1; {a/a, Simplify[a]/a, b/b == Simplify[b]/b} {1, 0, True} This one line "proof" that ...
14
votes
3answers
395 views

Clever use of DownValues, or failure to understand the “Mathematica Way.”

I needed to look at the changes in the values of about 4000 items from one year to the next. I have a table with identifiers and values for each year. Not all of the items are in each list. The ...
5
votes
1answer
49 views
2
votes
1answer
121 views

How to properly define this function of function

I encountered real problem at first, and here is the toy example variable argument stored some expression that is generated from other parts of the program. I ...