Create an symbol array

Question

Juan Miguel 2011-12-1

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编辑： Karan Gill 2017-2-21

Hello!!

I want to create a symbolic matrix in my Matlab( version R2010a), I have searched how could do it. I have seen this sentence:

A = sym('A', [3 4])

But when I write it in my Matlab, I receive this message:

??? Error using ==> error Formatted arguments cannot be non-scalar numeric matrices.

Error in ==> sym.sym>assumptions at 2180 error('symbolic:sym:sym:errmsg1','Second argument %s not recognized.',a);

Error in ==> sym.sym>tomupad at 2148 assumptions(S,x,a);

Error in ==> sym.sym>sym.sym at 114 S.s = tomupad(x,a);

I don't know why this sentence doesn't work when I have got it from a Matlab Document.

Could someone help me?

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Answer 1

Andrei Bobrov 2011-12-1

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long way :)

m = 3;
n = 4;
[a b] = ndgrid(1:m,1:n);
p1 = regexp(sprintf('A_%d_%d,',[a(:)';b(:)']),',','split');
p2 = cellfun(@sym,p1(1:end-1),'un',0);
A = reshape([p2{:}],m,[])

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Karan Gill 2017-2-21

编辑：Karan Gill 2017-2-21

Starting R2010b, this is wrong. See my answer below.

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Answer 2

Karan Gill 2017-2-21

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编辑：Karan Gill 2017-2-21

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Starting R2010b

>> A = sym('A',[2 3])
A =
[ A1_1, A1_2, A1_3]
[ A2_1, A2_2, A2_3]
>> A = sym('A%d%d',[2 3])
A =
[ A11, A12, A13]
[ A21, A22, A23]
>> A = sym('A_%d%d%d',[2 3 2])
A(:,:,1) =
[ A_111, A_121, A_131]
[ A_211, A_221, A_231]
A(:,:,2) =
[ A_112, A_122, A_132]
[ A_212, A_222, A_232]

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Answer 3

Steven Lord 2017-2-21

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This syntax is listed in the documentation online, which is the documentation for the most recent release (currently release R2016b.) But that documentation includes functionality that is not present in your release, such as the ability to create symbolic matrices. The Release Notes indicate that functionality was introduced in release R2010b (see the first item in the section of the Release Notes to which I linked.)

I don't believe there is a way to create a symbolic matrix like Karan showed in your release, short of manually creating the elements and concatenating them (as the "Creating Symbolic Variables and Expressions" page in the Getting Started section of the Symbolic Math Toolbox documentation for release R2010a shows.)

syms a b c;
A = [a b c; c a b; b c a]

If possible I recommend upgrading your software as there have been many enhancements to both MATLAB and Symbolic Math Toolbox in the past seven years or so. You can see a list of some of those enhancements if you change the upper element of the Release Range on the Release Notes page to which I linked to R2016b.