eqn = sym() not working

%first define the variables
title 'graph of the forcing function';
ezplot( heaviside(t-pi) + (-1)*heaviside(t-10), [0 15]);%graphing the forcing function
ylabel y; xlabel t;
syms s t Y %first define the variables
eqn = sym(('D(D(y))(t) + 3*D(y)(t) + 2*y(t) = heaviside(t-pi) + (-1)*heaviside(t-10)'));
%defining the differential equation
lteqn = laplace(eqn , t, s);%find the laplace transform
neweqn = subs(lteqn , {'laplace(y(t),t,s)' , 'y(0)', 'D(y)(0)'} , {Y,1,0});%put initial conditions into laplace transform 
ytrans = solve(neweqn, Y);%solving the Laplace transform for Y
y = ilaplace(ytrans , s, t)%finding the inverse laplace transform
ezplot( y , [0 15]);%plot the laplace solution on interval 0<t<15
title 'graph of Laplace Transform Solution for y" + 2y` +2y = h(t)';
ylabel y; xlabel t;

the output is as follows:

Error using sym>convertChar (line 1557)

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 1273)

S = convertChar(x);

Error in sym (line 229)

S.s = tomupad(x);

Error in Problem_Set_E (line 105)

eqn = sym(('D(D(y))(t) + 3*D(y)(t) + 2*y(t)

= heaviside(t-pi) + (-1)*heaviside(t-10)'));

Answer 1

[Shashank Gupta]

Hi Aric,

As the error message says, the function "sym" does not support a character array or a string, if you want to convert such datatypes to symbolic variable, all you need to do is use str2sym function as suggested in the error message.

I hope this helps.

Cheers