If there is a method to define the size of unknown vector x rather than this ???

I want to define the size of x vector, rather than this.. x=sym('x%d%d', [27 1]) where my size is 27*1

Answer 1

[John D'Errico]

x = sym('x',[27,1]);

[M.Shaarawy]

If there is other this better as my problem is...

I want to minimize function using PSO algorithm..

My function in matlab is..

function y=costfun(x) load A.mat;% matrix 27×27 load b.mat;% vector 27×1 y=norm(A*x-b,2);

So, now how to define the size of x in way to make MATLAB undetstand x size rather than sym , and not give me error due to to * inner matrix dimension must match ...as it stored A from load command as 27×27..

Thanks

[Karan Gill]

Post your full code and data. Your question is not clear otherwise. If you get an error, try a search for the error message to understand what is happening.

[M.Shaarawy]

function y = simple_fitness(x) load A.mat; % 27*27 matrix load obs.mat; % 27*1 vector y=norm(A*x-obs,2);

Answer 2

[Steven Lord]

If you're passing a function handle to costfun into some optimizer, you don't have to create x in your code (and you should not do so.) The optimizer will pass an x it has created into your function as the input argument and you just need to use it.

As an efficiency note, I would avoid calling load inside your objective function. Your objective function is likely to be called many times and all that disk access will take time. Call load twice outside the function and pass the variables you loaded into your objective function as extra parameters using one of the techniques described on that documentation page.