how to create symbolic vector?

hi. im using MATLAB version 7.9.0 (R2009b) and i would like to create symbolic vector. it should go like that: a=sym('a', [1 10]), where second argument means the length of the vector. but it doesnt want to work; error occurs: Formatted arguments cannot be non-scalar numeric matrices. how should i do it/any other way? thank you.

Answer 1

[Azzi Abdelmalek]

v=['[' sprintf('a%d,',1:10)];
v(end)=']'
a=sym(v)

[Vicky]

great, thanks.

[Francesco Giuseppe Fornari]

Hi,

how would you build a vector with groups simbolic of variables?

e.g.

(x1, y1, z1, x2, y2, z2, x3, y3, z3...)

thanks!

[Francesco Giuseppe Fornari]

I solved by doing this:

stot=[' '];
for i=1:12
    A = i;
      s1=sprintf(' x%d, ',A);
      s2=sprintf(' y%d, ',A);
      s3=sprintf(' z%d ',A);
      stot=strcat(stot, s1, s2, s3);
end

Fext1=['[' stot ']'];
Fext=sym(Fext1)

and it was working, but now I get the following message:

Warning: Support of character vectors will be removed in a future release. Character vectors can be used only for variable names and numbers. Instead, to create symbolic expressions first create symbolic variables using 'syms'.To evaluate character vectors and strings representing symbolic expressions, use 'str2sym'.

Doesn't seem to me that str2sym works for what I want...

Answer 2

[Walter Roberson]

That format for "sym" was not supported until (I think it was) R2011b.

a = sym(zeros(1, 10));

should work, I think.

[Vicky]

yes, but it creates 0-s... i want symbolic values. thanks, i have done it.

Answer 3

[Nicola Sacco]

Hi everybody,

with reference to Azzi Abdelmalek answer, it is possilbe to generate automatically also the symbolic variables in the vector?

I mean, the code

v=['[' sprintf('a%d,',1:2)];
v(end)=']'
a=sym(v)

produces

a =

[ a1, a2]

but neither a1 or a2 are symbolic variables, althoguh you can perform calcula with them (diff(..,a(1)) is allowed. How to get them without typing

a1 = sym('a1')

I need to assign numeric values to them, after some calculating a Jacobian with results to be something like

J = a1*a2;

Thanks in advance

[Azzi Abdelmalek]

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[Walter Roberson]

syms(sym('a', [1 2]))

However if you are generating variable names instead of assigning them, then it is bad practice to hard-code the names in expressions such as a1*a2 .