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
299 views

Skip one step of the loop if there is an NIntegrate::eincr message

Is there a possibility of skipping one step of a loop if in this step there appears an error like NIntegrate::eincr? After skipping, the loop should go to the next ...
0
votes
2answers
2k views

Defining a function in terms of matrix elements

Currently trying to use elements from a matrix in defining a function however having some trouble. This is a somewhat simplified version of the problem. Say I have the matrix ...
16
votes
2answers
1k views

Why do certain values in ArcSin not fully evaluate?

This is a continuation of: Why do certain fractional values in TriangleWave not evaluate? The analysis by R.M and rasher revealed that problem to reduce to the behavior of: ...
3
votes
2answers
179 views

Evaluate in Plot leads to function error

Please help - I'm really struggling to understand why this evaluates with errors. ...
0
votes
0answers
17 views

Evaluating a String that is a Variable [duplicate]

I have a Variable assigned a value, say ImportantDocuments=1 How do I make N["ImportantDocuments"] evaluate to be 1 instead of ImportantDocuments I found that ...
9
votes
2answers
362 views

Understanding Villegas-Gayley

Temporary message: I have written another question about the behaviour the code by Oleksandr R. . Sadly I clicked "discard" and that was lost. I am a bit demotivated now and in order to not let the ...
3
votes
1answer
120 views

Why is held expression evaluated?

Context: I'm studying non-linear dynamics. As part of a bigger problem, I'd like to generate lists of the form {{deq, ic1}, {deq, ic2}, ...}, where ...
4
votes
0answers
260 views

DynamicModule, SaveDefinitions and global functions

Unfortunately, I had not checked stackoverflow, because there, the exact same behavior was already reported. Please see the Q&A "SaveDefinitions considered dangerous". Up-front, I'm on Ubuntu ...
5
votes
1answer
363 views

Evaluation order control

This question is related to Evaluation order of Button[]'s action Concusion was, Button[]'s actions are evaluated in preemptive link so "the code that needs ...
2
votes
1answer
235 views

Piecewise function with user-input interval

I would like define a function g[data,bins,x] which is a piecewise constant function taking value data[[i]] in the range ...
2
votes
1answer
146 views

Need help looping a notebook evaluation

I'm a new user and would like to find the minimum value of soln1[30] obtained after repeating the following evaluation (below) for 1000 cycles (for instance). I can obtain sequential values of ...
3
votes
2answers
179 views

Keep data in memory inside a notebook without having to evaluate it again [duplicate]

I have a notebook that calculates some data in a relatively large time so I want to keep these data saved inside the notebook without recalculate them every time I open the notebook. I know I can ...
0
votes
3answers
96 views

Preventing evaluation until all undefined symbols are resolved

FixedPoint[If[# <= 0, 0, # - 1]&, 2 x] Causes an infinite loop because of 'x'. How do i automatically prevent evaluation until ...
2
votes
1answer
83 views

Need to run evaluation 2 times

Why does this only work after running the evaluation 2 times? ...
2
votes
1answer
114 views

Manual CellGrouping option causes crash at cell evaluation

Update: Try to reproduce this behaviour with CellGrouping set to manual. To do that: either evaluate ...
10
votes
1answer
123 views

Aborting from inside a ScheduledTask

If you have an Abort[] inside a ScheduledTask expression, what does it abort? The scheduled task evaluation, or any main kernel ...
2
votes
1answer
73 views

Evaluate only one from a set of procedures

Let's say I've got a list of procedures: {Print[1];, Print[2];, Print[3];} And I want to only evaluate 3rd one: ...
3
votes
3answers
140 views

Using a variable to tell Mathematica which existing variable to manipulate

I have an estimation routine I have coded up, I want now to do some tests on it where I pick a particular parameter and run the estimation for differing values of that parameter. What I want is to be ...
3
votes
2answers
195 views

Assigning an equation as a variable

I am compiling a calculator where many slider parameters are used to define a value, where the defined value may then be reused to define another value. I am unable able to, or at least been ...
2
votes
1answer
174 views

Differentiating a function that has NIntegrate within it

I am something of a novice with Mathematica. I have written the following code; ...
0
votes
1answer
153 views

Solving NLODE with substitution

I am trying to get a solution to a non-linear ODE, below is the code that works for my problem. ...
11
votes
1answer
269 views

TimeConstrained dynamic change of maximum time

I would like to run a time consuming function: TimeConstrained[f[x],maxseconds] and be able to change maxseconds during running (increasing or decreasing max ...
11
votes
3answers
231 views

Creating a custom context with a Hold construct

I'm trying to create a function "InContext" to execute a piece of code inside a certain context (and to return the result of evaluating that piece of code). One approach is to place the code inside a ...
2
votes
3answers
445 views

GraphPlot only working when I evaluate twice

I have some code that builds a graph and some vertex coordinates, but when I evaluate it I get a message that the list of coordinates is not valid and the graph is not valid and it shows the output as ...
6
votes
2answers
247 views

Remove versus ClearAll

What is the difference between Remove and ClearAll? I thought that "not being recognized by Mathematica", which is the effect ...
2
votes
3answers
164 views

Dynamic plot with Evaluate on expression

I'm trying to make a make a plot of a table of expressions, which should be pre-evaluated (since they are infinite series with analytic sums). I'm able to make the plot normally with ...
1
vote
1answer
130 views

Caching data in Mathematica package

Consider the following: m=Quantity[1,"meter"] If I run the package, it will return 1m But when I load the package, the ...
12
votes
3answers
257 views

Selective evaluation of blocks of code in a Manipulate

Is it possible to attach certain pieces of code to certain controls in a Manipulate? For example, consider the following Manipulate ...
0
votes
1answer
197 views

Plot[ D[Sin[x]] ] and Evaluate[] [duplicate]

Why does t = 2 Pi; Plot[D[Sin[x],x], {x,0,t}] (* Plotting the derivative of Sin[x] *) not work, but ...
7
votes
3answers
258 views

Why does Mathematica not seem to know that $i^x$ cannot be equal to $0$?

I am experiencing a curious behaviour of Simplify when handling expressions involving powers of $\mathbf{i}$, such as $\mathbf{i}^x$ where $x$ is unknown. For ...
1
vote
1answer
211 views

Passing a joined list of symbols for Module or Block to treat as its own local symbols

The Question I'd like to write a function which itself takes a list of symbols, e.g. Foo[{x, y, z}] to pass to Module ...
5
votes
1answer
774 views
0
votes
1answer
92 views

Plot producing many error messages when given complicated function

I'm new to Mathematica and am running in to all sorts of silly difficulties with coding in it. I'm trying to calculate a function f[x, k], normalise it with another ...
2
votes
1answer
300 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: ...
12
votes
4answers
356 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
50 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
93 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
142 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
173 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. ...
2
votes
1answer
61 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 ...
8
votes
2answers
1k 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
421 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
158 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
214 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 ...
3
votes
1answer
343 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 ...
20
votes
1answer
224 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 ...