How to I create an Array of Operations?

Hello,

I am trying to randomly iterate optimiser variables for an image registration problem. To do this I want to randomly choose one of the optimiser variables, then change its value and measure any improvements (or lack thereof). In my case I am using these four variables:

   a = randi([100,500]);
   b = 1e-6 + (1e-2 - 1e-6).*rand(1);
   c = rand(1);
   d = 1e-5 + (1e-3 - 1e-5).*rand(1);

My idea was to create an array of the four characters, then choose one at random, and run that operation. This is what I have so far:

 var_array = ['a' 'b' 'c' 'd'];
 r = randi([1 4],1);
 var_array_opt = var_array(r)

This would then randomly output either 'a' 'b' 'c' or 'd'. If 'c' were chosen for example, then I would want my function to perform the task assigned to variable c. I am unsure of how to do this last part, does anyone have any ideas?

Answer 1

[Stephen23]

It is not very clear what you want, but perhaps a cell array of function handles might help:

>> C{1} = @() randi([100,500]);
>> C{2} = @() 1e-6 + (1e-2 - 1e-6).*rand(1);
>> C{3} = @() rand(1);
>> C{4} = @() 1e-5 + (1e-3 - 1e-5).*rand(1);

And then simple select using indexing and evaluate that function, e.g.:

>> C{2}()
ans =  0.0083177
>> C{4}()
ans =  0.00069951

[Alex Poppe]

This is exactly what I wanted, thank you!

I apologise for the vague question I posed, to attempt to clarify:

I wanted a way to randomly pick one of the four functions that I listed and perform that function and not the others.

I didn't know that you could simply load all four functions into an array and randomly call different elements of that array to perform those function, so thanks again for your help!

Answer 2

[madhan ravi]

var_array = {'a' 'b' 'c' 'd'};     %edited after sir Walter's comment
r = randi([1 4],1)
var_array_opt = var_array{r}

[Walter Roberson]

This only gets a direct benefit if the variable names start having multiple characters, but using cell array would get the same benefit.

[Walter Roberson]

Consider

var_array = ['a' 'b' 'c' 'd' 'theta'];

Using var_array(r) would retrieve a single character such as 'a', 'b', 'c', 't' rather than one variable name. If you are using single character variables then var_array = ['a' 'b' 'c' 'd']; works fine though it tends to mislead as to how it could be modified.

Now var_array = {'a' 'b' 'c' 'd'} ; and using {} indexing has no problem with multicharacter variable names.

You do not need syms for either situation. Using syms will not give you any advantage towards selecting a task according to the selected variable. The information about which task to select is already encoded into r and using syms does not change that.

[madhan ravi]

Thank you sir Walter

Answer 3

[Walter Roberson]

Tasks = {@atask,@btask,@ctask,@dtask} ;

Thistask = Tasks{r} ;