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 Comments
Accepted Answer
Star Strider
on 16 Jun 2016
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 Comments
Rik
on 2 Sep 2022
What is your issue with that? It creates an empty array of the uint8 datatype, exactly as was asked.
Walter Roberson
on 2 Sep 2022
"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 ??
More Answers (5)
Lucas Hilden
on 22 Jan 2020
have no clue
2 Comments
James Tursa
on 12 Nov 2020
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++.
Walter Roberson
on 22 Jan 2020
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,
0 Comments
Walter Roberson
on 12 Dec 2021
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.
0 Comments
Hoang Truong
on 19 Mar 2023
syms theta;
R=[cos(theta) sin(theta)];
>> R
R = [cos(theta), sin(theta)]
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