Support for Multiplication and Transpose of Block Matrices of Symbolic Matrices?

17 次查看（过去 30 天）
FingersCrossed
FingersCrossed 2023-3-20
评论： ZHEN CHEN 2024-7-8
Ran in:
Does MATLAB not support multiplying and transposing block symbolic matrices? For instance, the following multiplication and transpose are not evaluated on the individual matrices inside of the block matrices:
syms A B C D E F G H [2 2] matrix
X = [A B;C D].'
X = 
Y = [A B;C D]*[E F;G H]
Y = 
The outputs I am expecting are:
X = [A.' C.';B.' D.']
X = 
Y = [A*E+B*G A*F+B*H;C*E+D*G C*F+D*H]
Y = 

请先登录，再回答此问题。

采纳的回答

Walter Roberson
Walter Roberson 2023-5-23
Ran in:
Does MATLAB not support multiplying and transposing block symbolic matrices?
No, it does not. Most operations are postponed on symmatrix. Some operations are performed immediately though
syms A(x) [2 2] matrix
syms B [2 2] matrix
syms Z [2 2] matrix
Z(:) = 0
Z = 
X = [A B; Z A']
X(x) = 
diff(X, x)
ans(x) = 
  1 个评论
FingersCrossed
FingersCrossed 2023-5-23
Thanks, hope to see this get added in the future. I've been unable to find a competitor's software capable of doing this either, though maybe I just don't know the right syntax.

请先登录，再进行评论。

更多回答（1 个）

Suraj
Suraj 2023-5-23
Greetings,
Based on your inquiry, I understand that you are trying to multiply and transpose block matrices of symbolic matrices.
MATLAB does support multiplying and transposing block symbolic matrices, but I think in your example, the reason why the expected outputs are not obtained is because there is a syntax error in the matrix declaration.
When you declare the matrices A, B, C, D, E, F, G, H, you need to use the sym function instead of syms. The syms function is used for declaring multiple symbolic variables, while sym is used for declaring a single symbolic variable or a matrix of symbolic variables.
Here is a workaround for that:
% Declare symbolic matrices
A = sym('A', [2 2]);
B = sym('B', [2 2]);
C = sym('C', [2 2]);
D = sym('D', [2 2]);
E = sym('E', [2 2]);
F = sym('F', [2 2]);
G = sym('G', [2 2]);
H = sym('H', [2 2]);
% Transpose of a block matrix
X = [A B; C D].';
% Product of two block matrices
Y = [A B; C D] * [E F; G H];
% Display results
disp('X =')
disp(X)
disp('Y =')
disp(Y)
This code should give you the desired results.
Regards,
Suraj
  2 个评论
FingersCrossed
FingersCrossed 2023-5-23
编辑：Walter Roberson 2023-5-23
Thank you for your reply, though this is not what I am trying to do. I would like to operate on A, B, C, D as symbolic matrix variables as in my example and not on an element by element basis. Examples of these operations for non-block matrices are given at:
https://www.mathworks.com/help/symbolic/use-symbolic-matrix-variables.html
Walter Roberson
Walter Roberson 2023-5-23
Ran in:
The syms function is used for declaring multiple symbolic variables, while sym is used for declaring a single symbolic variable or a matrix of symbolic variables.
That is not correct.
The sym function is primarily intended as a function that returns a single symbolic expression without itself assigning to any variable . So sym('A', [2 2]) returns a symbolic array for whatever purpose you need; you can assign it to a variable if you want.
The syms function is primarily intended for command syntax that builds one or more symbolic expressions and assigns them to variables . So syms A [2 2] functionally does A = sym('A', [2 2]) . But syms can also create symbolic functions, such as syms f(x) and with the matrix keyword creates symmatrix
Note the difference:
syms A [2 2]
syms B [2 2] matrix
A
A = 
B
B = 
whos A B
Name Size Bytes Class Attributes A 2x2 8 sym B 2x2 8 symmatrix
Without the matrix keyword, the variable A becomes a matrix containing symbols A1_1, A1_2, A2_1, A2_2 whereas with the matrix keyword, B becomes a 2 x 2 symmatrix . A symmatrix is treated differently than a sym matrix:
A * magic(2)
ans = 
ans.'
ans = 
B * magic(2)
ans = 
ans.'
ans = 

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Mathematical Functions 的更多信息

标签

产品


版本

R2022b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by