How to solve a system of equations symbolically? (MATLAB R2011a)

This is what I'm trying to do:

    syms x1 x2 x3 X1 X2 X3 t

    S = solve('x1 = 3*t*X1+X2', 'x2 = 2*t^2*X2', 'x3 = 5*t*X3')
    S = [S.X1 S.X2 S.X3]

I get a reference to non-existent field error though.

It's solving for x1, x2, and x3, but need to solve for X1, X2, and X3 in terms of x1, x2, x3 and t.

Please help! Thanks!

Answer 1

    syms x1 x2 x3 X1 X2 X3 t
    S = solve(x1==3*t*X1+X2, x2==2*t^2*X2, x3==5*t*X3,X1,X2,X3)
    S = [S.X1 S.X2 S.X3]

That gives me this error:

??? Error using ==> char Conversion to char from logical is not possible.

Error in ==> solve>getEqns at 189 vc = char(v);

Error in ==> solve at 67 [eqns,vars] = getEqns(varargin{:});

Error in ==> practice at 11 S = solve(x1==3*t*X1+X2, x2==2*t^2*X2, x3==5*t*X3,X1,X2,X3)

VERSION OF MATLAB?

try this

    clear
    syms x1 x2 x3 X1 X2 X3 t
    S = solve(x1==3*t*X1+X2, x2==2*t^2*X2, x3==5*t*X3,X1,X2,X3)
    S = [S.X1 S.X2 S.X3]

R2011a did not support using == in symbolic expressions. I think it was R2011b that first supported that.

S = solve('x1=3*t*X1+X2', 'x2=2*t^2*X2', 'x3=5*t*X3','X1','X2','X3')

Then no need to use syms

Yes, correct. If everything is quoted, syms is not needed.