Error in using syms

So I have this code

syms x t s X F

F=laplace('diff(x(t),t,t)+5*diff(x(t),t)+610*x(t)-exp(-t)',s);

F=subs(F,{'laplace(x(t),t,s)'},{X});

F=subs(F,{'x(0)','Dx(0)'},{0,0});

x=solve(F,'X');

x=ilaplace(x);

I'm using Matlab 2020a. It gives me this error:

Error using sym>convertChar (line 1546)

Character vectors and strings in the first argument can only specify a variable or number. To evaluate character vectors and strings representing symbolic expressions, use 'str2sym'.

Error in sym>tomupad (line 1262)

S = convertChar(x);

Error in sym (line 229)

S.s = tomupad(x);

Error in transform (line 22)

if ~isa(f, 'sym'), f = sym(f); end

Error in sym/laplace (line 28)

L = transform('symobj::laplace', 't', 's', 'z', F, varargin{:});

What should I change in this so that I get the required output?

Answer 1

[Star Strider]

Remove the single quotes, define ‘x’ as ‘x(t)’, and define ‘Dx’ (and ‘D2x’ if you want to), explicity:

syms x(t) t s X F 
Dx = diff(x);
D2x = diff(Dx);
F=laplace(D2x+5*Dx+610*x(t)-exp(-t),s);
F=subs(F,{laplace(x(t),t,s)},{X});
F=subs(F,{x(0),Dx(0)},{0,0});
x=solve(F,X);
x=ilaplace(x)

producing in LaTeX format —

The code is otherwise unchanged.