How do I define a variable without assigning it a value?
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I just want to define a variable, f without assigning any values to it so I can use it in an equation.
3 个评论
James Tursa
2016-6-16
编辑：James Tursa
2016-6-16
Do you mean symbolically? E.g.,
syms f
Or maybe you mean an anonymous function? E.g.
myfunction = @(f)f+3
João Santos
2021-12-12
without syms, whats the best option?
Image Analyst
2021-12-12
@João Santos, see Star's answer below.
采纳的回答
Star Strider
2016-6-16
You can also assign a variable as an empty matrix, cell, string (or any other empty value):
x = []; % Empty Scalar, Vector Or Matrix
y = {}; % Empty Cell
z = ''; % Empty String Or Character
5 个评论
Muhammad Asif Aziz
2018-10-12
how can defne int variable?
Walter Roberson
2020-1-22
w = zeros(0,0, 'uint8'); %empty variable but uint8 datatype
or
w = uint8([]); %empty variable but uint8 data type
Chris
2022-9-2
this just assigns '[]' as the variable lol.
Rik
2022-9-2
What is your issue with that? It creates an empty array of the uint8 datatype, exactly as was asked.
Walter Roberson
2022-9-2
"exactly" what was asked was "without assigning any values to it so I can use it in an equation"
Assigning an empty array to a variable is assigning a value to it (the empty value), and does not form something that can be used to create equations (in the sense of being able to solve or numerically solve the equation)
The supported answers to create something to be used in "equations" include
- Symbolic Toolbox -- sym() and syms()
- Problem Based Optimization -- optimvar()
- I am fairly unclear on the details, but maybe Deep Learning "dlarray" might arguably qualify in this category? https://www.mathworks.com/help/deeplearning/ref/dlarray.html ??
更多回答（5 个）
Lucas Hilden
2020-1-22
4 个投票
have no clue
2 个评论
Allison Noe
2020-11-12
me too
James Tursa
2020-11-12
MATLAB is a dynamically typed language. You create the variable by assigning it a value. You don't need to create or type it ahead of time like you do in compiled languages such as C/C++.
Hoang Truong
2023-3-19
2 个投票
syms theta;
R=[cos(theta) sin(theta)];
>> R
R = [cos(theta), sin(theta)]
Azzi Abdelmalek
2016-6-16
1 个投票
Walter Roberson
2020-1-22
0 个投票
You can use James' File Exchange contribution https://www.mathworks.com/matlabcentral/fileexchange/31362-uninit-create-an-uninitialized-variable-like-zeros-but-faster to create an uninitialized array. The initial contents of the variable will be whatever happened to be in memory,
Walter Roberson
2021-12-12
0 个投票
If you are trying to set up an optimization problem, sometimes it is easier to do it by expressing relationships between variables. You might be able to take advantage of Problem Based Optimization
In some cases, equations that you might not think of normally as being optimizations can be rewritten: the expression A(x) == B(x) can potentially be rewritten in terms of minimizing (A(x)-B(x))^2, so if you have the Optimization Toolbox but not the Symbolic Toolbox, then this approach has some potential.
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