Function to find max value from function cell array

Hi there,

I have a 3 elements cell array:

A{1} = @(y) {1*y};
A{2} = @(y) {2*y};
A{3} = @(y) {3*y};

And I want to create a function that will output the maximum value of all 3 elements of A. The below is not working for y=3 or any value of y:

B = @(y) cellfun(@(x) max(x), A{1,:}(y), 'UniformOutput', false);
B(3)

any ideas?

Thanks in advance

[Adam]

Assuming vx is an array of inputs to apply each function to something more like this, off the top of my head:

B = cellfun(@(func) max(func(vx)), A, 'UniformOutput', false);

[Spyros Polychronopoulos]

Hi Adam I had a typo there I meant to type y in that line not vx. I am sorry for the confusion.

[Adam]

Ok, but where is y coming from? Is it known at the time you call this or is it another variable input? If it is variable at the time you call the cellfun then I don't think you can use cellfun for this as you would be essentially running over two-dimensional inputs to create the answer. If it is known then just replace vx with y in the code I wrote.

[Spyros Polychronopoulos]

Unfortunately it is not known that is why I want to create B as a function of variable y.

The idea is that B would be an objective function for an optimizer.

[Adam]

Well, actually that should be fine:

B = @(y) cellfun(@(func) max(func(y)), A, 'UniformOutput', false);

should work. As y is just passed as a fixed variable to the cellfun rather than one that the cellfun itself is trying to operate over.

[Spyros Polychronopoulos]

I tried that already. Is this working for you?

A{1} = @(y) {1*y};
A{2} = @(y) {2*y};
A{3} = @(y) {3*y};
B = @(y) cellfun(@(func) max(func(y)), A, 'UniformOutput', false);
B(3)

Answer 1

[Alex Mcaulley]

I see to possible answers depending on what you want:

If you want to obtain the maximum value (for the three functions) for each y:

A{1} = @(y) 1*y;
A{2} = @(y) 2*y;
A{3} = @(y) 3*y;

B = @(y) arrayfun(@(y) max(cellfun(@(func) func(y), A)),y);

y = [1,2,3,4,5]
B(y) = 
ans =

     3     6     9    12    15
     

If you want the maximum value of each separate function for all values of y the answer is the one given by @Adam:

B = @(y) (cellfun(@(func) max((func(y))), A, 'UniformOutput', false))
y = [1,2,3,4,5]
B(y) = 
ans =

  1×3 cell array

    [5]    [10]    [15]