Problem using subs in syms with matrix

 syms a b q;
c=q*a+b;
d=c(1);
e=c(2);
f=c(3);
a=[1 2 3]';
b=[4 5 6]';
q=[1 9 0;
    2 3 4;
    3 5 4];
c=subs(c)
d=subs(d)
e=subs(e)
f=subs(f)

The variable c will be a 3X1 matrix and I wanna extract the individual elements for further operation. Please Help!

I get the error

??? Error using ==> mupadmex Error in MuPAD command: Index exceeds matrix dimensions.

Error in ==> sym.sym>sym.subsref at 1381 B = mupadmex('symobj::subsref',A.s,inds{:});

Error in ==> Untitled2 at 5 e=c(2);

Answer 1

[Andrei Bobrov]

b = sym('b',[3 1])
a = sym('a',[3 1])
q = sym('q',[3 3])
a1 = [1 2 3]';
b1 = [4 5 6]';
q1 = [1 9 0;
     2 3 4;
     3 5 4];

d = c(1)
d = subs(d,[a(:);b(:);q(:)],[a1(:);b1(:);q1(:)])

[Saurav Agarwal]

Thank you

[rajasekhar reddy ogirala]

error msg to below program in image is

Error in sym/subsref

B = mupadmex('symobj::subsref',A.s,inds{:});

in line 41

gp = eval(f(z)/(f(z)-f(y)));

Answer 2

[Alexander]

The error raises in these lines:

 d=c(1);
 e=c(2);
 f=c(3);

The variable c is a (1x1) sym and MATLAB cannot access the 2nd or 3rd element. From the code I guess, you want to substitute q by some values? If I'm wrong, please let me know what you want to achieve by c(1), c(2), and c(3). Following I assume you want to substitute q:

If you have R2012a you can use symfuns for that:

 syms a b q c(q);
 c(q)=q*a+b;
 d=c(1);
 e=c(2);
 f=c(3);
 a=[1 2 3]';
 b=[4 5 6]';
 q=[1 9 0;
     2 3 4;
     3 5 4];
 d=subs(d)
 e=subs(e)
 f=subs(f)

If you have an older version, you have to substitute q:

 syms a b q;
 c=q*a+b;
 d=subs(c, q, 1);
 e=subs(c, q, 2);
 f=subs(c, q, 3);
 a=[1 2 3]';
 b=[4 5 6]';
 q=[1 9 0;
     2 3 4;
     3 5 4];
 d=subs(d)
 e=subs(e)
 f=subs(f)

[Saurav Agarwal]

Thanks for the reply.

I guess my question wasn't clear enough.

q is a 3x3 matrix and a & b are 3X1 matrix.

so my c should be a 3X1 matrix

i wanna store the three elements of c in d, e and f so that i can carry out further calculations in syms representation itself.

the substitution is at the end of code.

I hope i am clearer this time.

syms a b q;

c=q*a+b;

d=c(1);

e=c(2);

f=c(3);

%..... operations on d e and f

%...

%...

a=[1 2 3]';

b=[4 5 6]';

q=[1 9 0;

2 3 4;

3 5 4];

c=subs(c)

d=subs(d)

e=subs(e)

f=subs(f)

[Saurav Agarwal]

Is there a problem with the declaration of variables a b and q. ?

Please Help!