Error using sym>convertChar (line 1459)

I need some help of my code. What's wrong with this code ?

>> clear all; clf

>> syms y t x z

>> % input a unit-step (heaviside) response

>> y = dsolve('D2y + 5*Dy + 6*y = heaviside(t)','y(0) = 0','Dy(0) = 0','t');

Error using sym>convertChar (line 1459)

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 1225)

S = convertChar(x);

Error in sym (line 214)

S.s = tomupad(x);

Error in dsolve>mupadDsolve (line 327)

sys = [sys_sym sym(sys_str)];

Error in dsolve (line 189)

sol = mupadDsolve(args, options);

>>

I attach dsolve.m and heaviside.m with this form.

this is my code.

original code from this

Answer 1

[Uriel Gabriel Zapata Rodríguez]

i have the same problem with this code and nobody is here :'(

a=input('Enter the function in the form of variable x:','s');

x(1)=input('Enter Initial Guess:');
error=input('Enter allowed Error:');
f=inline(a)
dif=diff(sym(a));
d=inline(dif);
for i=1:100
x(i+1)=x(i)-((f(x(i))/d(x(i))));
err(i)=abs((x(i+1)-x(i))/x(i));
if err(i)<error
break
end
end
root=x(i)

[SL: Formatted code as code]

[Steven Lord]

First, you shouldn't use error as the name of your variable. It already has a meaning in MATLAB.

Second, you shouldn't use inline. If you want to convert the text the user has entered into a function, use str2func to turn it into a function handle. If you want to convert it into a sym object use str2sym.

Answer 2

[Uriel Gabriel Zapata Rodríguez]

%newton-raphson method

a=input('Enter the function in the form of variable x:','s');

x(1)=input('Enter Initial Guess:');
error=input('Enter allowed Error:');
f=inline(a)
dif=diff(sym(a));
d=inline(dif);
for i=1:100
x(i+1)=x(i)-((f(x(i))/d(x(i))));
err(i)=abs((x(i+1)-x(i))/x(i));
if err(i)<error
break
end
end
root=x(i)

Answer 3

[Steven Lord]

As stated in the Note at the top of the documentation page for dsolve "Support for character vector or string inputs will be removed in a future release. Instead, use syms to declare variables and replace inputs such as dsolve('Dy = y') with syms y(t); dsolve(diff(y,t) == y)."