keep getting error when trying to take Laplace transform

trying to find laplace for homogenous equation : cI′′ + dI′ + I/e = 0

syms D2I DI I gensoln deq t s
deq = 'c*D2I + d*DI + (1/e)*I';
ldeqdiff = laplace(deq,t,s);
ldeqdiff=subs(1deqdiff)

keep getting error :

ldeqdiff=subs(1deqdiff)

↑

Error: Unexpected MATLAB operator.

Answer 1

[Walter Roberson]

You have

ldeqdiff = laplace(deq,t,s);

which assigns to a variable name that begins with a lower-case 'L'. Then you have

ldeqdiff=subs(1deqdiff)

which attempts to subs() on an expression that begins with the digit 1 not with a lower-case 'L'.

deq = 'c*D2I + d*DI + (1/e)*I';
ldeqdiff = laplace(deq,t,s);

laplace() has never been documented as accepting a character vector -- not even in the days when the Symbolic Toolbox was based upon Maple instead of MuPAD.