Questions tagged [evaluation]
Questions about how Mathematica evaluates expressions, tracing evaluation (Trace*), handling expressions in unevaluated form (Hold*, Unevaluated), nonstandard evaluation, etc.
1,154
questions
3
votes
0answers
57 views
How to plot function with pattern-matched argument and catch-all definition that throws
Consider the following function:
f[n_?NumericQ] := n;
f[args___] := Throw[{args}];
Then try to plot it:
...
1
vote
1answer
22 views
Substitution in delayed evaluation function [duplicate]
I am trying to do the the following: precomputing an expression and then making a function out of it. It has to be delayed evalution, because some of the parameters are only known when the function is ...
0
votes
1answer
43 views
Power towers Power towers from x to n [on hold]
How can I make Mathematica calculate a power tower for a succession of numbers, but instead of writing them, Mathematica does the iterative calculation.
...
0
votes
0answers
46 views
Plotting works with @ but not with […] [closed]
Why is it that I can plot the function of a series if i define it with @:
f1[x_] := Normal@Series[f[u], {u, 0, 2}] /. u -> x
but not when I define it with [......
0
votes
1answer
31 views
Order of evaluation of variable
I'd like to control the order of evaluation in a multi-variable function.
Example: Suppose I have the function:
B[x_, y_] := x + y/x;
If I try to evaluate ...
2
votes
1answer
63 views
Problem with numerical evaluation of a Hankel identity
There an identity with the Hankel functions of both types (https://dlmf.nist.gov/10.11 eq. 10.11.4 or http://apps.nrbook.com/bateman/Vol2.pdf pg. 80 eq. 43):
$$
\sin\left(\nu\pi\right){H^{(2)}_{\nu}}\...
4
votes
0answers
40 views
Run computation in separate process and kill it after a time limit
I am looking for a solution to run a Mathematica calculation in a separate process (separate kernel) and cancel the computation after a given time. If it cannot be cancelled, then just kill that ...
0
votes
1answer
29 views
Testing Expression over region of values
I'd like to test whether this expression is negative when a and b are constrained to lie within (0,1) interval. Any ideas how?
...
0
votes
2answers
86 views
Only evaluate assignments in a notebook
Maybe I'm not using the best programming practices in Mathematica, but my notebooks usually contain a mixture of "definitions" and "computations" with these definitions. Say,
...
0
votes
2answers
30 views
Plotting 3-d function using Evaluate and Table
I want to plot $z(F, x, \lambda)$ where I fix a few values of $F$ and $\lambda$ and see how it varies with $x$. With 2-d functions, I could vary the second parameter easily using a combination of <...
3
votes
1answer
35 views
Prevent argument substitution in held expression when injecting into unevaluated code
I want to write a custom sow/reap pair to wrap any piece of code in sow[code] and call reap ...
0
votes
1answer
30 views
How to have NonlinearModelFit not evaluate a function too early?
This is a follow up of my previous question How can I define the following function for arbitray values of the arguments? that received no attention so here I will try to be more concise with the ...
0
votes
0answers
43 views
1
vote
0answers
40 views
InverseLaplaceTransform does not evaluate [closed]
I am very new to Mathematica and not a mathematician, so the question may be very trivial.
I am trying to find the function $f(t)$ such that
$\qquad e^{-e^{s}} = \int_0^{+\infty} e^{-st}f(t)dt$,
...
1
vote
0answers
35 views
How to speed up the evaluation of a sum of incomplete Gamma functions?
We need to do a ContourPlot for the following function $H[x,y,n]$:
...
3
votes
1answer
112 views
An alternative to (%%…%) (k times) [closed]
Sometimes it may be useful to use (%%…%) (k times) to get the kth previous result in a notebook instead of setting a variable.
However, if I want to get the 8th previous result, for example, I would ...
0
votes
1answer
49 views
Getting unexpected results form If expressions [closed]
I'm mystified by this:
g[a_, b_, c_] :=
Module[{d},
d = If[(b < 1), b, b + 1];
If[a < b, d = 0.];
d*c]
g[a, 20, 40]
...
11
votes
1answer
156 views
2
votes
1answer
137 views
Why would Evaluate[] in Plot give me warning about precision?
I have a code:-
Plot[Evaluate@PDF[NormalDistribution[1.6, 0.2], x], {x, -6, 6}]
And then I got the warning: ...
3
votes
2answers
83 views
Construct a function that maps strings to functions
The main question is the last 5 lines (including codes) of this article.
A[x_, y_] := Evaluate[ToExpression["x^2+y^2"]]
A[3,4]
Then the output becomes
...
1
vote
1answer
61 views
How to get ReplaceAll to happen before function call
I have a problem I am attempting to solve with NMinimize.
I have a scoring function, which will give me a final score. The problem has many variables, so instead of having them as parameters, they ...
0
votes
2answers
45 views
Using MinValue with NDSolve
A simplified example looks like this. The basic idea is to maximize fHelper by adjusting \[Alpha] for each ...
0
votes
1answer
50 views
How can I define the following function for arbitray values of the arguments?
Consider the following function
a[m_, l_] = 1/Log[m/l];
with this function I define
...
0
votes
0answers
58 views
Mathematica does not evaluate large expression
I want to apply Conjugate[] to a certain quite long rational function of some parameters. My problem is that although it evaluates perfectly fine on each single part of the expression, Mathematica ...
2
votes
1answer
30 views
How can I keep the argument of TeXForm[Integrate[1/Sqrt[1 + x], x]] from being evaluated?
How can I keep the argument of TeXForm[Integrate[1/Sqrt[1 + x], x]] from being evaluated?
This is what I am getting:
...
1
vote
1answer
34 views
How to interpret a string as a multiline cell of expressions
I need a string like the following:
"2+2
\"Hello
world\"
3+3"
to be evaluate like
2+2
"Hello
world"
3+3
Note that ...
0
votes
1answer
34 views
Unable to operate on the table imported from .mx file
I saved a table by exporting it to .mx file. Now, when I import it back, it gives me the desired output. So, to work with elements of the table, I first define the imported table as (res2 = Import["...
14
votes
3answers
276 views
Evaluated vs. unevaluated Association
This question might have a remote connection to my older question, it is also about sameness of expressions and subtle differences observable only in certain forms.
I encountered this strange ...
8
votes
2answers
159 views
Using `With[…]` with a list specification as a variable [duplicate]
If you have some defined function, say f[a_, b_ c_, x], one can initialize this by using With[...] as
...
1
vote
2answers
56 views
Why does sol[r][[1]] become r?
This is a follow up to this question. This answer is great it gives the correct solution and I can plot it, but I have a problem: when I try to integrate the solution in this way:
...
2
votes
2answers
82 views
InterpretationBox problem with symbolic expressions
Related to this question,
Why does this InterpretationBox construct work when x, y are ...
4
votes
1answer
45 views
Evaluate calls my function multiple times when the function generates an error
If I execute a line of code with Evaluate I find some unexpected behavior when the code returns an error. Here is a minimal example. Let ...
3
votes
1answer
59 views
Combining `With`, `If` and SetDelayed
I just noticed that
With[{x = 1}, If[x == 0, 0, 1]]
returns 1 (as I expected) but
...
3
votes
1answer
117 views
function evaluation - I don't get it
this function returns Pi/4 for a[1,4]
In[...]:= a[r_, n_] :=
Module[{an = Pi/n, h = r Cos[an], w = 2 r Sin[an]}, an];
a[1, 4]
Out[...]= Pi/4
so the kernel ...
6
votes
1answer
100 views
Suppressing analytical evaluation in NDSolve
I am trying to find a numerical solution to a set of coupled ODEs with NDSolve. Let us say $\boldsymbol{X}$ is a vector, and $\boldsymbol{F}$ is a non-linear vector ...
0
votes
0answers
63 views
How to see/trace Manipulate steps?
I am relatively new in Wolfram Language. What I want to solve is tracing "manipulate" steps in one of the demonstration project example codes. In my particular example, there are nearly 20 user build ...
6
votes
2answers
124 views
How to define a functional that produces at runtime a function by evaluating selected parts in its definition?
Consider the following functional as an example:
...
4
votes
1answer
124 views
Evaluate an expression at singular points
I have
y[x_] := 1/Sqrt[2] (5 - x - Sqrt[8 - (x + 1)^2])
{x0, x1} = {-1 - Sqrt[8], -1 + Sqrt[8]};
and I want to calculate
...
0
votes
0answers
37 views
Run only a part of a notebook
Is it possible to run only a part of a notebook?
I have a long notebook which takes forever to evaluate, so I was wondering if it was possible to run only a couple of cells instead of the whole ...
0
votes
1answer
52 views
How to evaluate a function on Imported data (.xlsx file)
I have imported an excel file, and I want to evaluate an expression on each point:
Data = Import["data.xlsx"]
which gives output like this:
...
4
votes
1answer
53 views
Evaluate in place annoyance
I want to use the following expression to get a string value:
Row[{"Enter index identifier: ", InputField[Dynamic[indexidentifier], String]}]
and I also want to ...
3
votes
1answer
88 views
6
votes
1answer
47 views
Why does `$Pre` need to be defined indirectly via some other function?
The documentation for $Pre gives the following example
...
5
votes
2answers
84 views
Obtaining head and parts without evaluation
I have been trying to write a routine MyHead and MyPart
which would have the following properties.
MyHead[2+3]
evaluates to Plus
...
0
votes
1answer
54 views
Evaluation functions with lower and upper limit ODE?
How do I find the numerical value of y at 0 and also at 1. Here is my code. I appreciate any help.
...
1
vote
1answer
42 views
Respecting excluded index in sum
I'm using a function involving a sum where some indices are excluded:
...
0
votes
2answers
53 views
Can anyone please help me to plot the following list of complex values?
I tried to plot the complex values in Mathematica using the following code
...
0
votes
2answers
60 views
Why is this not False? (SameQ,Equal, Set) [duplicate]
How can we understand why Mathematica does not evaluate this expression to False?
{{1, 2, 3, 4}, {4, 3, 2, 1}} == 0
1
vote
1answer
82 views
ReleaseHold and Get
I've created a try.m file which has the following structure:
{
Hold@{a+b+c},
Hold@{a^2+b^2}
}
On my main code I do:
<...
3
votes
2answers
100 views
Inconsistency between Plot and NIntegrate
Have a look at the following definition
Y[q_, w_ /; w < 0] := 0
Y[q_, w_] := w
The function Y is zero for negative ...
