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

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2
votes
1answer
212 views

Why is this expression being held, and how can I evaluate it?

I can't figure out why an expression isn't evaluating, even though there's no Hold* in its FullForm: ...
11
votes
4answers
309 views

Using With to scope over pure functions

Consider this example: given an option for a function func as "x" :> (a&), how can one assign different values to ...
1
vote
1answer
40 views

Output cell written with NotebookWrite dissappears on whole notebook evaluation, yet remains if I individually evaluate it

Create a new notebook with the following two input cells: NotebookWrite[EvaluationNotebook[], Cell[BoxData[ToBoxes[Manipulator[Dynamic[x]]]], "Output"]] and ...
0
votes
1answer
77 views

Evaluate outer function first

I'm new in Mathematica so this is maybe super easy to do, but I can't figure out how. I've got a function plus[a,b] that sums two numbers and I need to implement a ...
7
votes
3answers
118 views

How to stop a single function to be evaluated?

See this example: AA = {x} \[Function] Normalize[x] BB = {x} \[Function] Evaluate[AA[x]*5] I need BB to be Normalize[x]*5. Some context:I call evaluate because ...
0
votes
1answer
107 views

Order of evaluation in nested expression

I am trying to make a function that works as follows: Integrate 1 for all t in the interval $ [0,1] $ such that the first element of function vstar is positive. ...
0
votes
0answers
55 views

CreateDocument using a specific Evaluator (Kernel)

I was trying to build a button to create a new document that contained a dynamicaly changing table. In the parent notebook i am using another kernel - not the usual "Local". The problem is that in the ...
2
votes
1answer
51 views

Label cell goes away with SelectionEvaluate

When a given cell has a label (given with the CellLabel->"label" option of the cell), then this label disappears after calling SelectionEvaluate[ nb ] when the ...
6
votes
2answers
379 views

Obtaining the name of a variable as a string [duplicate]

Suppose that I have an arbitrary variable myVariable. Is there some function fun -- either built-in or one that I can define -- ...
15
votes
8answers
393 views

Is it possible to use RandomChoice to choose without other choices being evaluated?

I'm trying to do this: i1 = 1; i2 = 1; RandomChoice[{ (i1 = i1 + 1), (i1 = i1 - 1), (i2 = i1 + 1), (i2 = i2 - 1)}] In order to chose randomly which ...
2
votes
1answer
106 views

Reuse local variable in declaration within With [duplicate]

Considering the richness of Mathematica.SE, I am quite surprised I could not find my answer... I am very sorry if it is a duplicate. Consider the following example: ...
7
votes
6answers
197 views

How to join held Lists?

Let's say I have a = Hold@{2+2} b = Hold@{4+4} How can I get Hold@{2+2,4+4} ie join the two held lists ? More ...
2
votes
1answer
181 views

Manipulate executes expressions multiple times

I am using Manipulate for a rather intricate front end for data visualization. I was getting very sluggish performance and was able to boil the problem down to a ...
17
votes
1answer
183 views

How to get Cases to wrap results in an arbitrary head?

A number of functions provide for results to be wrapped in an arbitrary head. This is very important in cases where the results should not be evaluated. Take ...
2
votes
3answers
325 views

Select sublists with second element nearest to zero

I've got some big lists from which i need some data (one of the big lists). To be specific, I need to divide this biglists in sublists of the same length (10000), and form a new list with the mean of ...
7
votes
1answer
256 views

How to force an evaluation to use only one core?

There are some evaluations which are automatically parallelized or multithread if there are cores available.( for example, Eigenvalues) But I don't want the ...
4
votes
3answers
432 views

Prevent Mathematica to automatically evaluate Manipulate at start

I'm using an initialization cell to import a lot of data: data = Import[myFiles]; and then I use a custom function to display this data with Manipulate: ...
13
votes
5answers
636 views

How are parameters evaluated for a Plot in Manipulate

I am trying to get my head around how Manipulate evaluates functions in a Plot. I have read the introduction to Manipulate, and introduction to Dynamic, but I still ...
8
votes
1answer
168 views

Why is building a table of function values so much slower than just plotting the function?

Here is a function that take some time to evaluate: n = 1000; coeffs = RandomVariate[NormalDistribution[], n]; f[x_] := Sum[coeffs[[k]] Sin[k x]/k, {k, 1, n}]; ...
2
votes
1answer
190 views

is there a method to send different cell evaluation to different core

I am running Mathematica on a computer with mulicpu and every cpu has multicore. I am wondering if there exist a method to send different cell evaluation to different core? So if I already have a ...
2
votes
1answer
282 views

Use output of NDSolve as an integration limit of NIntegrate

I've been working on a ODE, for a function y[t], that, due to it's complexity, has to be solved numerically. I then need to use the results of NDSolve, which I ...
2
votes
2answers
166 views

While loop doing cell evaluation not completing

I am trying to get a loop structure using While to repeatedly evaluate another cell referred to in its body (using a cell tag). ...
2
votes
0answers
75 views

Assign variables from list inside With or Module

I have found that it is possible to assign variables from lists, as follows. In[1]:= r = {1, 2, 3}; In[2]:= {a, b, c} = r; In[3]:= b Out[3]= 2 However, if I try ...
0
votes
1answer
379 views

Can graph interpolating function, but not use it. Any thoughts?

When solving a system of differential equations numerically, I get two interpolating functions. I can graph both of these, but when I try to evaluate either of the functions at a point, it just spits ...
0
votes
1answer
131 views

Understanding output of multivariable integration

I'm new to Mathematica and I'm trying to integrate this function: ...
5
votes
2answers
621 views

Possible to evaluate only selected cells?

Is it possible to evaluate only the selected cells programmatically that I am interested in? Say in current cell to bottom of the notebook, instead of evaluate notebook or cells?
3
votes
3answers
146 views

HoldForm: how does it interact with nested evaluations?

Here's an example to illustrate the issue I'm having. right = 8 - y; left = y^2 + 6; integrand = HoldForm[Evaluate[right]] - HoldForm[Evaluate[left]] (I ...
10
votes
3answers
175 views

Pattern matching on Orderless functions inside Hold

MatchQ[Hold[1 + 2], Hold[2 + 1]] returns False. But in the presence of a Blank[] in the ...
2
votes
2answers
3k views

Step-by-step definite integration

I am interested in obtaining the intermediate steps for rather straightforward symbolic definite integrations (e.g., from an elementary calculus text). As an example, for $\int_0^1 x\,dx$ I'd like ...
3
votes
1answer
348 views

How can I save the current evaluation state of a notebook and start from it later?

I currently have a nested Table command running (in Mathematica 9), with two progress bars to track the variables. I have to shut down or hibernate the computer in ...
1
vote
2answers
54 views

Get the unevaluated expression from a numbered cell

If a cell exists as below: In[1] := (xyPoints = {{1,2},{2,5},{3,10}}; ListLinePlot[xyPoints]) Is it possible to get at the expression rather than the plot shown ...
22
votes
1answer
623 views

How do you set attributes on SubValues?

SubValues, as discussed in a previous question, are declared as follows ...
2
votes
0answers
110 views

Force Dispatch to generate dispatch tables

Dispatch creates hash tables only for lists of length larger than 3. Is there any way to force MMA to create hash tables even for lists of length smaller than 4? ...
5
votes
1answer
145 views

Why does this pattern with Plus not work for numbers?

I have a very simple question about redefining basic built-in functions, such as Plus. I'm pretty sure someone must have asked a similar question around here, but I ...
0
votes
1answer
237 views

Pull Constants outside of integrals

I would like Mathematica to pull constants outside of an integral: e.g., $\int_0^t f[t] g[s] dt \to g[s] \int_0^t f[t] dt$ This has previously been discussed at replacement rule to pull independent ...
6
votes
1answer
291 views

PlotStyle does not work when plotting a non-evaluated list of functions [duplicate]

When a list of functions is passed to Plot in an unevaluated form (e.g. with Through), the result is a plot with single color. ...
2
votes
1answer
111 views

NotebookWrite undo

Is there way to make NotebookWrites undooable? For example let's say I open a new notebook and then run. ...
1
vote
1answer
414 views

The underlying process of Integrate[] [duplicate]

Integrate[x^4 E^-x^2, {x, 0, +∞}] Output: (3 Sqrt[π])/8 Can someone explain to me the specific calculation process ?
20
votes
1answer
250 views

How does Return work?

It is not completely clear to me how Return[] works. The documentation says: Return[expr] returns the value expr from a ...
7
votes
2answers
448 views

How does Mathematica determine that an evaluation should be terminated?

How exactly does Mathematica determine that evaluation of particular expression should be finished and the result should be returned? Here are some examples of unclear behavior which have arisen, ...
39
votes
3answers
808 views

The clearest way to represent Mathematica's evaluation sequence

WReach has presented here a nice way to represent the Mathematica's evaluation sequence using OpenerView. It is much more clear way to go than using the standard ...
7
votes
1answer
157 views

The Flat Attribute, Unevaluated and the Evaluation Process

To make this question easy to follow let's give some symbols a couple attributes. Attributes[f] = {Flat}; Attributes[s] = {Orderless}; Now consider the ...
1
vote
2answers
106 views

Evaluation of elements in a list and then sorting them

This is probably a simple problem, but I'm having a lot of issues with it because I'm unfamiliar with Mathematica syntax. I have a list ...
4
votes
2answers
135 views

Equivalent of __FILE__?

Many languages define a special identifier whose value is the path to the source file currently being processed. (For example, in C, this is done through the ...
11
votes
2answers
299 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 ...
4
votes
1answer
194 views

Manipulate a Plot that contains a variable that contains symbol [duplicate]

This snippet mm = m Manipulate[{mm, Plot[mm x, {x, 0, 1}]}, {m, 0, 1}] (m is not defined anywhere) produces a sadly fixed ...
1
vote
2answers
156 views

How can I speed up this plot manipulation? Why does Evaluate not help?

If I were able to "Save" the computed inverse function somewhere and then plot it, the manipulation would become faster. As I understand, Evaluate should do the job, but for some reason it does not. ...
1
vote
1answer
104 views

About evaluation in Block

I'm completely puzzled by the following codes: Clear[func, f] a = x^2 + z; func[k_] := Block[{f}, (f[x_] := Evaluate[(a /. {z -> k})]; f[1])] func[2] ...