Creating a Simbolic vector and setting assumptions on it

Hi,

I'm trying to build a symbolic vector with variable dimension N, and I would like it to be real...

I managed to build the vector with the desired lenght throug str2sym, but I don't know how to set assumption "real" on its variables.

(I would like to use this vector for a linear system).

stot2=[' ']; 
for i=1:N
    A = i;
      s1=sprintf(' u%d, ',A);
      s2=sprintf(' v%d, ',A);
      s3=sprintf(' w%d ',A);
      stot2=strcat(stot2, s1, s2, s3);
end

U1=['[' stot2 ']'];
U=str2sym(U1)

Thanks for any help!

Answer 1

[Walter Roberson]

u = sym('u', [1 N], 'real');
v = sym('v', [1 N], 'real');
w = sym('w', [1 N], 'real');
U = [u, v, w];

[Francesco Giuseppe Fornari]

thanks!

This work. But I want the count for each triplet u,v,w in the final vector:

u1, v1, w1, u2, v2, w2, u3, v3, w3

How would you do this?

[madhan ravi]

 reshape([u;v;w],1,[])

[Francesco Giuseppe Fornari]

thanks, it works perfectly!

Answer 2

[Divya Gaddipati]

You can declare assumptions on symbolic variables using the assume function from the Symbolic Math Toolbox. For more information on how to use this function, refer to this link.

In your code, since “U” is a sym object, you can directly loop over U and set each of the variable to real.

for i = 1 : length(U)
    assume(U(i), 'real');
end

[Walter Roberson]

Yes, but there is no need to loop:

assume(U, 'real');