Creation and evaluation of a variable containing a variable in reasonable time

I am currently trying to get a fast code that is as flexible as possible but i am facing a problem that is apparently tricky :

I want to create a variable matrix A that changes in time.

let's assume

A = [1 -t; 2 t];

If i did not specify time in advance this line will crash. but at the same time i do not want to specify it as it will change.

One could tell me to instenciate this matrix A AFTER changing my time, like

t = 3;
A = [1 -t; 2 t];

but I actually want this time dependant matrix to be a user input ! Thus i'll have the matrix A before anything else in my program.

using the symbolic toolbox is a way but a really slow one. indeed :

syms t
A = [1 -t; 2 t];
t = 3;
tic;
eval(A);
toc;
Elapsed time is 0.002917 seconds.

whereas

t = 3; 
tic; 
[1 -t; 2 t]; 
toc;
Elapsed time is 0.000014 seconds.

So is there a fast way to do something like that (knowing that i am running on ODE function thus i really need the evaluation to be performed on a reasonable time).

There is the annonymous function possibility as

A = @(t) [1 -t; 2 t];
t = 3;
tic; A(t); toc
Elapsed time is 0.000233 seconds.

Which seems to be the in-between solution, but can such a function be passed as an argument to a function?

My idea was to create a unassigned variable t and then create my variable A then re-evaluate the compiled version of the variable A, but i don't even know if this is a possible/doable solution

Answer 1

[Oleg Komarov]

The handle solution:

A = @(t) [1 -t; 2 t];
B = @(x) A(x) 

B(3)

Answer 2

[Walter Roberson]

If you use the symbolic solution, instead of using eval(A) you should use subs(A) or (more likely) double(subs(A))

[Oleg Komarov]

Just subs is enough but somehow the handle solution is faster on my pc, Win32 r2010b

[Walter Roberson]

subs() would give back a symbolic number; double() is needed to convert it to double precision to be on equal terms with the handle approach.

[Oleg Komarov]

That's what I expected too, but with r2010b I get:

syms t

A = [1 -t; 2 t];

subs(A,3)

isnumeric(ans) % 1