# Tagged Questions

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

233 views

### Evaluate code to some point

How can I evaluate my code, up to some point? I don't want to evaluate all of my code always. I have to use Shift - Enter for every line from the first cell up to the point I want to be, and it's not ...
514 views

### How to pass a list of arguments into HoldAll

I have a list of arguments (which in reality is lengthy): arguments = {a, b, c} arguments2 = {a_, b_, c_} f[Sequence@@arguments2] := a + b + c Note: It seems ...
49 views

### Define a Plot3D function with custom options [duplicate]

I am trying to define a Plot3D function with custom options, following (this previous SE question), but I'm running into a brick wall. I've narrowed the problem to the following 'toy' code: ...
57 views

### Confusing efficiency and evaluation when returning pure functions? [duplicate]

I have a function that takes some time to evaluate, that's meant to be a polynomial approximation to a function. The polynomial is defined by a list of coefficients, so I have the function "polynomial"...
215 views

### How do I evaluate the terms in an expression, but not the expression itself?

I am trying to write a set of homework questions. I would like the output to evaluate the constants but not the sum, so that I may present the homework question as something like this: \sum_{n=1}^...
419 views

### NumericQ prevents evaluation at a numerical value sometimes

I set up a symbolic integral, to be evaluated only when some of the symbols have been replaced by numbers. The evaluation after assigning numbers to the symbols is still symbolic for some reason. The ...
169 views

I'm having some trouble with identical code giving different answers. On a fresh kernel (MM 9.0.0.0, Windows 64-bit), running the same code, copy-paste, gives two different answers: ...
458 views

### Why won't ContourPlot accept a variable argument? [duplicate]

I have a list of linear inequalities which describe a (polygonal) region. I can use RegionPlot to visualize this region; but I'd also like to overlay this plot with ...
2k views

### Keep function range as a variable

Plot[2*x^2 - x + 2, {x, -1, 1}] plots a function of x from -1 to 1. As far as I can see, I cannot "save" this range in a variable: ...
126 views

I'm trying to get this expression to display as typed instead of evaluating the 1/1.121. ...
663 views

### Forcing evaluation of ArgMax

How to force evaluation of ArgMax before its output gets used in Solve? Background: I'm trying to solve for the Nash ...
455 views

### Evaluate Numerator and Denominator Separately

I have this function. ...
803 views

### How is the Mathematica kernel structured internally, and how does evaluation work?

There is so much information available for Java--the internal details of (for example) the JVM memory manager are well-documented, and the performance considerations arising from its interaction with ...
534 views

### A is fast, B is fast, but together they're Mathematica-crashing slow?

I'm trying to do something with finding solutions to a quantum mechanics problem with n wells. If there are 40 wells, I need to find the solution to an equation in the form: ...
382 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 ...
120 views

### Strange double evaluation using MorphologicalGraph

(MMA 9.0.0 on Mac OS/X 10.8) Please consider the following snippet (this is as SMALL as I could make it -- my attempts at making a smaller repro-case eliminated the effect that I am investigating) <...
445 views

### Exclude Sections/Subsections/… from evaluation

I'm working on a large notebook and I want to exclude some sections and subsections from being evaluated when I evaluate the whole notebook. Is there a way to exclude specific sections or ...
412 views

### Summation of If statements

The following made me curious. Suppose you want to sum the if statement If[x[i] < 1., x[i]^2, 0.] over i=1,2, i.e. ...
241 views

### Evaluation order of Button[]'s action

it looks like it should be well known issue but I haven't found answer anywhere. Please tell me why the result (after clicking) of this: ...
1k views

### Behavior of expression evaluation in Plot

I'm confused with Mathematica's way of parsing expressions. I've been struggling with this for a while and never found an exhaustive answer, sometimes things don't parse the way I think they would ...
407 views

### Get the approximate analytical solution to an algebra equation

Is there a way to get the analytical form to the root of this equation: 2 A e (-ArcTanh[smax/s0] + ArcTanh[(smax Cos[w ζ])/s0]) == F0 ...
354 views

### Log function - why is Log[b,b] not being evaluated to 1?

Have been experimenting with the Log function to demonstrate simple Log relationships such as Log[xy], Log[x+y] etc. ...
225 views

### Strange Behavior with RegionPlot

Consider the following code. RegionPlot[Print[{x, y}], {x, -2, 2}, {y, -2, 2}, PlotPoints -> 2] ...
184 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 ...
143 views

### UpValues evaluation with Dot operator

I would like to simplify some database notation, and I'm doing some tests with UpValues for that. For example, if I set this Upvalue fot tab1: ...
413 views

### Make Mathematica wait before replacing?

How can I force Mathematica to completely evaluate a subexpression before using a replacement rule? For example, consider the following definition (for the series of ...
156 views

### how to print stack trace when TimeConstrained times out

According to the documentation, TimeConstrained generates an interrupt which interrupts the computation. This interrupt is treated just like an abort, at least in ...
484 views

### Evaluation of OptionValue[]

I have a function that takes an OptionsPattern and I want to access several options, say a, and ...
447 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 ...
558 views

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### Why does Evaluate[a[[1]]]=0 assign a value to a variable while a[[1]]=0 doesn't?

I'm trying to do a small page counter with Mathematica, for leting me know about my reading progress on some books. I'm stuck on a problem: ...
160 views

### Function to preserve evaluation on display?

I'm looking for a function that applies the following behavior to an expression: -When the expression is given as the full input, or as part of a function that cannot be evaluated, it remains in ...
227 views

### Why does Dynamic output cause CPU usage when onscreen?

I write such a line in Mathematica: {Slider[Dynamic[s]], Dynamic[f[x_] := s*x]} After evaluation, the CPU immediately runs at full power. And if you scroll the ...
442 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. <...
379 views

### Evaluating a Recursive Expression

Why does this raise an error ...
108 views

### Different behaviour of ValueQ inside and outside of a loop

I need to store a rather big number of variables and I tried to do that by storing each variable as Z[n] with varying n. I guess this was not my best idea. The first problem I encountered is when I ...
1k views

### How can I set a keyboard shortcut to run a command?

I want to use this to add a keyboard shortcut to an undo function I wrote. The basic problem is the following: I have a command, let's say x=1, and I want to run ...
5k views

### How do you force a decimal output? [duplicate]

I have some very small values such as 2.601519253*10^-8. I'd like to output these values to CSV for another program to work with. I've tried N[value, 50], but Mathematica still insists on producing ...
328 views

### Return partial result when MemoryConstrained aborts NDSolve

I use NDSolve to solve a large set (~400) of coupled ODEs. Sometimes, the memory (~4GB) gets filled up, and my computer becomes impossible to work with, because it ...
546 views

### Get the name of a symbol passed to a function

I'm trying to get the name of a symbol passed to a function with this: f[x_] := {SymbolName[x], x} SetAttributes[f, HoldFirst] x = 5; f[x] But ...
271 views

### Button's command is not evaluated in iteration

I wish I didn't feel like a newbie after several months, but... If I enter the following: Table[ Button[ "Number: " <> ToString @ i, Print @ i], {i, 1, 5}] ...
201 views

### Obtain input expression from history without evaluating

I typed and evaluated an expression, but deleted it from the notebook. For instance, suppose it was In[1]:= Round@SessionTime[] Out[1]= 2 I now want to retrieve ...