create indexes of x in a for loop

Hi all, I am trying to create and save some x values in an array in a format of A=[x(2)+x(3);x(3)+x(6);x(4)+x(9)];

so I tried something like that

for i=1:3
    
    y=@(x) x(i+1)+x(3*i);
    
end

however I get for each i the same expression,

y=@(x)x(i+1)+x(3*i)

Is there any way to do that?

thanks

Nikolas

Answer 1

[Stephen23]

It is not very clear what you are trying to achieve, but it is possible to store a function handle in a cell array:

C =  cell(1,3);
for k=1:3
    C{k} = @(x) x(k+1)+x(3*k);
end

Although to be honest it is not clear why you are defining a function handle at all. If x is already defined, why not just get the numeric values directly:

N =  nan(1,3);
for k=1:3
    N(k) = x(k+1)+x(3*k);
end

[Nikolas Spiliopoulos]

Hi again ,

thanks for the reply. I tried this but it still put the values with i, and not something like

A=[x(2)+x(3);x(3)+x(6);x(4)+x(9)]

well it's a long story why I am trying to do this keeping the x, it's because I am trying to create a for loop to create my objective function.

thanks again

[Stephen23]

It is not clear why you need a loop. Simple indexing would probably give what you are looknig for:

V = 1:3
A = x(V) + x(3*V)
A = A(:)

[Nikolas Spiliopoulos]

thanks for the prompt reply,

I am getting an error:

"Index exceeds array bounds."

thanks

[Stephen23]

"I am getting an error:"

Index exceeds array bounds

Then you are trying to access an element of x that does not exist.

Solution: do not try to access elements of x that do not exist.

[Nikolas Spiliopoulos]

well that's parft of the question,

if there is any way of indexing a variable x which value is not known.

thanks

Nikolas

[Stephen23]

"if there is any way of indexing a variable x which value is not known."

Of course it is possible to index a variable whos value is not known:

>> A = rand(4,4); % random matrix whos values I don't know
>> A(2,3) % index into it
ans =  0.77218

Now we know that value!

But it stands to reaon that you cannot retrieve the value of an element that does not exist.

I get the feeling that you don't want indexing, but perhaps you are trying to create a function of x. It would help if you explain a little about what you are actually trying to achieve here.

[Nikolas Spiliopoulos]

thanks for the answer again,

anyway my problem if there is any way to do symbolic indexing

for example

 A=[ x(1)+x(2) ; X(3)+x(4)]

maybe my question is not very clear

Nikolas

[Stephen23]

"anyway my problem if there is any way to do symbolic indexing"

What exactly is "symbolic indexing"?

Perhaps a simple function of x is what you are looking for... nothing to do with indexing at all.

[Nikolas Spiliopoulos]

well my problem is, if I have a symbolic variable x,

is it possible to create somehow something like

 A=[ x(1)+x(2) ; X(3)+x(4)]  etc.

by using an index i for example?