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

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12
votes
3answers
299 views

Arguments to If[] are not evaluated

I got bitten by the following: f[x_] := 3*x; g[x_] := If[Log[f[x]] < 0, f[x], 0]; g[x] Out[11]= If[Log[3 x] < 0, f[x], 0] where I thought the call to ...
8
votes
1answer
447 views

How to properly DumpSave & Get Global`s symbols inside packages while not touching Global context?

For efficiency reasons I prefer to use DumpSave instead of Save. For ease of access I prefer to save symbols in ...
10
votes
1answer
236 views

Old values are not freed/garbage collected when you re-evaluate an assignment

For this code: (* Cell 1 *) generate := Module[{x}, x = Range[100 * 1000 * 1000]; x]; (* Cell 2 *) g = generate[]; MemoryInUse[] If I evaluate cell 2 ...
5
votes
2answers
305 views

Manipulate Evaluation Order Problem

I seem to be getting some unintended results from a nested Manipulate that I have not been able to resolve. I boiled down the problem I'm having to a simplified ...
7
votes
1answer
278 views

Changing the plot variable inside Plot [duplicate]

Possible Duplicate: Difference in Plot when using Evaluate vs when not using Evaluate Assume one has vector of functions (e.g., vec={x,x^2}). The ...
5
votes
1answer
148 views

Impossible to bypass evaluation on returned values?

Following all the great advice on this other question, I'm now fluent with HoldAllComplete and Unevaluated on the input side of ...
10
votes
2answers
162 views

Subtle difference in conditional rules placement

I had gotten used to thinking of the placement of a condition in a rule definition as logically immaterial. In my specific example, namely ...
15
votes
4answers
611 views

Making a symbol's new definitions be tried before all previously defined ones

Is there any way to "close" a package (or a symbol, or a context) in that if a user of the package adds definitions to the symbol they will be tried before the package defined ones, just like what ...
8
votes
2answers
662 views

Mathematica rule substitution memory

First I present the specific programming question, and then I provide further background details. Given an expression in Mathematica, say f=3x+7y, there are two ...
8
votes
2answers
487 views

How to make Mathematica re-evaluate a cell after some event?

I am doing a little project to demonstrate something: ...
9
votes
2answers
304 views

Defining a ForEach function

Consider the following function definition: ForEach[iterators__] := Table[#, iterators] &; Two questions about it: I. It works perfectly if you call it like ...
1
vote
0answers
101 views

is there an equivalent of “show” steps? [duplicate]

Possible Duplicate: Get a “step by step” evaluation in Mathematica In wolfram alpha, when preforming for complicated integrals there's a 'show steps' option that explains how ...
8
votes
3answers
296 views

How to write a function-defining function which stores the function arguments in a stack?

I have a function-defining function SetAttributes[DefFn, HoldAll]; DefFn[f_[args___], body_] := f[args] := body; I am trying to modify this function to record ...
2
votes
1answer
647 views

A combination of Set::setraw and Set::shape errors

Please consider the following toy code: ...
8
votes
3answers
165 views

With/Function(/etc) replacement behaviour

Can anyone explain to me this behaviour? I've been having more than a couple of similar doubts these last weeks. For example f[_?NumericQ] := 8; Now, if I do ...
11
votes
3answers
353 views

Does AbsoluteTiming slow the evaluation time?

I've started using AbsoluteTiming to discriminate between similar function constructs, but I sometimes feel like it takes substantially more time to evaluate a ...
4
votes
2answers
189 views

Setting a lower limit on calculation time

Sometimes it can come in handy to set a lower limit for a calculation. Consider for example an animation that is generated by some infinite loop, which would run way too fast to display properly for ...
9
votes
3answers
3k views

General::ivar is not a valid variable when plotting - what actually causes this and how to avoid it?

I was just evaluating a couple of expressions and started to get errors like this: ...