MATLAB: Symbolic Equation Solver- should work, but doesn’t!

Question

Hi,

I have a matrix that includes terms using the symbol "s". I need the exponential of that matrix, and then the determinant of that, both in terms of s, which I then want to set equal to 0 to solve for s. For example:

syms s
F=[0,1,0,0;0,0,1,0;0,0,0,1;m*s^2/EI,0,0,0]
Y=vpa(expm(F))
Step2=det(4*Y)

So now I have a long equation in terms of the symbol s. According to the mathworks website http://www.mathworks.com/help/toolbox/symbolic/brvfu8o-1.html , I should be able to do this:

"Algebraic Equations with One Symbolic Variable

Use the double equal sign (==) to define an equation. Then you can solve the equation by calling the solve function. For example, solve this equation:

syms x
solve(x^3 - 6*x^2 == 6 - 11*x)
ans =
 1
 2
 3"

So I've defined s as a symbol, but when I use solve(Step2==0,s)

it gives me an error- essentially that symbol can't be used in a logic expression?

So what's the deal? Anyone have any idea why it isn't working? Thanks!!! Kaitlin

Answer 1

Just use

solve(Step2,s)

Note: the vpa() step probably is not doing you much good for accurate solutions. It might possibly make the solution faster, though.