# Is there any way to represent symbolic variables as I write from left to right?

2 views (last 30 days)
Edited: Paul on 19 Feb 2022
As you know in Matrix manipulation you're not allowed to change the order of Matrix. for example AB # BA (the commulative law is usually broken).
I was wondering if there was a way to represent the below matrix multiplication?
How can I modify this simple code to output the correct matrix ruls? ie change (BC/A) to (C/A)*B
syms I A B C D
sympref('MatrixWithSquareBrackets',true);
E=[1 0 ; -C/A 1]
E =
F=[A B ; C D]
F =
X=E*F
X =
Thanks a bunch!
Torsten on 15 Feb 2022

Paul on 16 Feb 2022
Since R2021a, one can define symbolic matrices. I haven't really used them too much and so don't know how to get any further than what is shown below. I'm surprised Matlab won't carry out the multiplication of the block matrices. Maybe there is another command that will do so.
syms I [2 2] matrix
syms A [2 2] matrix
syms B [2 2] matrix
syms C [2 2] matrix
syms D [2 2] matrix
E = [I zeros(2);-C*inv(A) I]
E =
F = [A B;C D]
F =
G = E*F
G =
Walter Roberson on 16 Feb 2022
You cannot. Block operations like that are not supported.
Perhaps I should not say "cannot", but rather "no method is provided". There might hypothetically be some way involving using mapSymType or similar operations.
Paul on 18 Feb 2022
Edited: Paul on 19 Feb 2022
That's too bad that block matrix multiplication isn't supported. Maybe that's coming in a future release.
It would also be cool if the identity matrix and the zero matrix could be created as special symmatrix constants with specified dimensions to be used in equations such as above.

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