Questions tagged [evaluation]
Questions about how Mathematica evaluates expressions, tracing evaluation (Trace*), handling expressions in unevaluated form (Hold*, Unevaluated), nonstandard evaluation, etc.
1,122
questions
4
votes
1answer
43 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
57 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
116 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
83 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
38 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
114 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
121 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
36 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
49 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
50 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
78 views
6
votes
1answer
45 views
Why does `$Pre` need to be defined indirectly via some other function?
The documentation for $Pre gives the following example
...
5
votes
2answers
83 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
49 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
41 views
Respecting excluded index in sum
I'm using a function involving a sum where some indices are excluded:
...
0
votes
2answers
49 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
57 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
98 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 ...
8
votes
1answer
2k views
What is -(-2,3,4)?
I was trying to define a function f such that, when its second argument is negative, we have
$$
f(a,b,c,d,\dots,n)=f(a,-b,-c,-d,\dots,-n)
$$
i.e., we reverse the ...
1
vote
1answer
95 views
How to Open, Evaluate and Close the same Notebook 100 times in a row?
I have a Mathematica notebook which I Open and Evaluate by hand. It Exports some data and then Closes.
I now wanna Open, Run and Close the exact same Notebook 100 or 1000 times in a row to get a lot ...
2
votes
1answer
52 views
Open, Evaluate and Close notebooks sequentially
I wanna Open, Evaluate and Close notebooks sequentially.
Code from question here
...
3
votes
3answers
325 views
How do pure functions differ from functions defined with SetDelayed?
Why is it that
f[{{a_, b_}, {c_, d_}}] := (a z + b)/(c z + d)
will return (2 + z)/(4 + 3 z) on evaluating ...
7
votes
0answers
74 views
How useful is $SynchronousEvaluation?
Example
SessionSubmit @ Print @ $SynchronousEvaluation
Will print False even though ref/SessionSubmit/Details last point:
...
2
votes
0answers
29 views
Do not evaluate function inside of another function for simplification
Consider the simple example :
ff[x_] := x^2
gg[x_] := (ff[x] - ff[-x])^2
Let's assume I would like to expand g[x_] as a polynome of ff[x] and ff[-x], but I don'...
12
votes
0answers
129 views
Scheduled tasks and dynamic updating
Here is an example:
x = 0; Dynamic[x]
now please run:
SessionSubmit[x = 1; Pause[10];]
Problems:
Annoying one: ...
0
votes
1answer
64 views
Evaluating function before its plotting
Suppose I want to plot a function $f(x,y)$ but first need to calculate its symbolic expression. An easy solution is to copy the output of my calculation by hand and then paste into ...
0
votes
0answers
27 views
Underflow and Machine Precision
I am using Mathematica to solve a system of differential equations and evaluate and plot the solutions on an interval. The solutions have non-zero solutions, but Mathematica underflows in a portion of ...
1
vote
2answers
57 views
NMaximize selects duplicate inputs and a problem with EvaluationMonitor
The aim of the following is to maximize 'penalty' and monitor it for convergence during the process:
...
0
votes
1answer
32 views
Constructing sequence of function with elements depending on the previous one / recursion
Starting from a function $\theta0[x\_ , y\_ , z\_ ]$, the terms $\varphi[x\_ , y\_ , z\_ ]$ constitutes a sequence of functions that is constructed as follows:
Order 1 (one function and its ...
0
votes
1answer
29 views
Evaluate list queries inside `HoldForm[]` terms
When I have an equation like (example)...
...I can derived it and turn it into TeXForm afterwards (that is what I want). Therefore, I might want to additionaly ...
0
votes
2answers
36 views
First ReplaceAll, then evaluate an expression
Here is a simple example using ReplaceAll:
rvec[[2]] /. rvec -> {x, y}
I think Mathematica first tries to evaluate ...
0
votes
1answer
46 views
Evaluation Control for Equation Input to NDSolve
I am trying to numerically integrate a system of equations using NDSolve and am having issues with symbolic matrix inversion taking a long time. The actual system is much more complicated, but I have ...
6
votes
1answer
66 views
New input cell style with a custom evaluator
I'm interested to implement a custom input style which would appear (mostly?) like a normal "Input" Cell, but which would ...
0
votes
0answers
16 views
SystemException[“MemoryAllocationFailure”] with long evaluation involving FindRoot
I had earlier posted my code in a previous question, but I am reposting my code here:
...
2
votes
0answers
92 views
Why was implementation of “Exponent” changed since version 11.3? [closed]
I have a following expression and need an exponent of n
Exponent[Exp[Sqrt[n]]*n^2, n]
(* 2 *)
Exponent[Exp[Sqrt[n]]*n, n]
(* 1 *)
All versions 7,8,9,10 up ...
0
votes
2answers
70 views
Can ComplexInfinity output be trusted?
A quick question regarding evaluation of algebraic expressions at specific values. If for instance I enter
(x + 1) (x + 2)/((x + 2) (x + 3)) /. x -> -2
...
0
votes
1answer
47 views
Why is this NDSolveValue function remembering past inputs?
I have been attempting to generate a function that uses NDSolveValue to return the value of a solution to a system of ODE's when an event condition is triggered, as a function of the initial ...
0
votes
1answer
54 views
Variable nesting depth inside table
I hope my title makes sense. The idea is the make a function in which a set of variables, $l_1$, $l_2$, etc. are accessible inside the innermost body of a nested (/folded) function. Each of these ...
8
votes
2answers
185 views
How to explain the behaviour of TreeForm?
Just try this:
g=1;a=1;TreeForm[Hold[g[a]]]
The weird thing in the outcome is that the node of g displays 1 ,and a is still a.
I do not know how to explain ...
0
votes
1answer
26 views
Comparison between Point And EmptyRegion
My aim is to evaluate the length of a line segment lying inside a sphere.
Code
...
0
votes
1answer
40 views
Function that refuses to return a value
I wanted to know the exact solution to the following differential equation
$$
\frac{\mathrm{d}^2 y}{\mathrm{d} t^2} = - \frac{1}{y-1}, \quad \begin{aligned} y(0) &= 0 \\ \left. \frac{\mathrm{d} y}...
4
votes
2answers
525 views
How to prevent Mathematica rounding extremely small numbers to zero?
I have a function that, while the maths itself is unimportant, at certain values it results in a very large number multiplying a very small number. E.g. 10^450000 * 10^-449998. As you can see, this ...
6
votes
1answer
119 views
RegionPlot3D no longer localizes its arguments?
Bug introduced after 9, fixed in 12.0.
Just now, I was astonished to find the behavior of RegionPlot3D changes somewhere after v9 . Consider the following sample:
...
0
votes
2answers
94 views
How to get the derivative with StepMonitor?
I am trying to use StepMonitor inside of the NDSolveValue function for a complicated system of differential equations, but the simple example below shows my issue just fine.
I am trying to obtain ...
6
votes
1answer
623 views
How to monitor a big program?
Is it possible to know how much % of calculations are done in a big program?
In other words, % will increase gradually when the calculations are progressing. I want to see the %.
5
votes
5answers
269 views
How to factor all coefficients of a multivariable into prime factors
I have several polynomials in 2 variables with integer coefficients, e.g.,
poly= -10 x - 10240 y^3 - 1520 x y^4;
I'd like to convert all such polynomials into a ...
12
votes
2answers
264 views
Unexpected behavior of the procedure `Area` on the object 'Polygon'
Bug introduced in 11.3 or earlier and fixed on 12.0.
Sometimes get a results, sometimes left unevaluated.
For instance
...
3
votes
2answers
86 views
Keep element of formula as it is
I have
ClearAll["Global`*"];
de = f''[y] - (n^2 \[Pi]^2)/(4 a^2) f[y];
DSolve[de == -q/S (4/(n \[Pi] b))(-1)^((n - 1)/2), f[y], y]
and I would like the $(-1)^{(n ...
2
votes
1answer
79 views
Why is Mathematica “de-evaluating” my expressions when I try to generate a Table? [duplicate]
I am attempting to plot a combination of StreamPlot and ParametricPlot that is a function of a parameter. When using Manipulate or Animate, the evaluation is slow but the graphs are outputted as ...
