problem with taking Differentiate from variable with counter !

dear all

i need to write a code that have x symbolic variable that contain x=[x1 x2 x3 .... xn] and also x is depended to variable t (time).at last i want to Differentiate from x. for 3 or 4 x it is easy to write code like below :

>> syms x1(t) x2(t) x3(t)
>> x=[x1 x2 x3]

x(t) =

[ x1(t), x2(t), x3(t)]

>> diff(x,t)

ans(t) =

[ diff(x1(t), t), diff(x2(t), t), diff(x3(t), t)]

now when i want to write code that contain 30 x it is difficult to this in this way

i also try this but it doesnt work :

>> syms t
>> x(t) = sym('x%d',[1 4])

x(t) =

[ x1, x2, x3, x4]

>> diff(x,t)

ans(t) =

[ 0, 0, 0, 0]

is there any way to do this in this way and if it is i also need a way to call the specific x

for example :

for i=1:3
for j=1:3
xij(t)=...
end 
end 

i know writing in this way is wrong but just for clearing my idea i really appreciated if someone could help me

Answer 1

[Birdman]

Well, the approach would be as follows:

n=30;
x=sym(zeros(1,n));%preallocation
syms t
for i=1:n
   x(i)=str2sym(sprintf('x%d(t)',i));
end

Now, you can easily take derivative of x as

 diff(x,t)

and observe the result you want.

[shahin hashemi]

ty for your attention mr birdman but i got this error :

Undefined function or variable 'str2sym'

i use matlab R2017a

[Birdman]

Then use sym instead of str2sym:

n=30;
x=sym(zeros(1,n));%preallocation
syms t
for i=1:n
   x(i)=sym(sprintf('x%d(t)',i));
end

[shahin hashemi]

Ty for your answer mr birdman i search and figure out that str2sym add to matlab in 2017b

i use sym and i got my answer but is there any benefit in useing this command is stead of sym