max_product that t takes v as vector and n as positive integer

My code that's not working. Please help

function [prodout,ind] = max_product(A,n)
  A=0;    
  prodout = exp( conv(log(A),ones(1,n),'valid') );
      if isreal(A), prodout=real(prodout); 
      end

[Wasi von Deutschland]

Answer 1

[Stephen23]

Method one: slidefun: Download Jos' excellent FEX submission slidefun, then you just need:

>> max_product = @(v,n)max(slidefun(@prod,n,v,'forward'))
>> [p,x] = max_product([1,2,2,1,3,1],3)
p =  6
x =  3
>> [p,x] = max_product([1,2,3,4,5,6,7,8,9,10], 2)
p = 90
x =  9

Method two: toeplitz:

>> max_product = @(v,n)max(prod(toeplitz(v(n:-1:1),v(n:end)),1));
>> [p,x] = max_product([1,2,2,1,3,1],3)
p =  6
x =  3
>> [p,x] = max_product([1,2,3,4,5,6,7,8,9,10],2)
p =  90
x =  9

[Wasi von Deutschland]

But if the arguments are [1 2 3 4 5 6 7 8 9 10], 2 then this function made an error. because max product at number 8 and index value is 2

[Wasi von Deutschland]

Could you please answer me?

[Wasi von Deutschland]

That's my assignment and how can I use that function to calculate value? I have to make a function that works the same way as slidefun.

[Stephen23]

See my edited answer.

[Wasi von Deutschland]

stephen I'm sorry but if arguments are [1 2 3], 4 ?? then

[Stephen23]

@Wasi von Deutschland: I am sure that you are capable of adding that into the function yourself (it is your homework after all, so you might like to actually put in some effort yourself, then you might actually learn something). You could use numel and if, here is an outline of what you need to write

function ....
if numel(...) < ...
   ...
else
   ...
end
end

[Wasi von Deutschland]

if numel(v)<n
product=0;
ind=-1;
end

[Wasi von Deutschland]

I really appreciate your effort

Answer 2

[Guillaume]

Another possible way:

slide = toeplitz(v(1:n), v);
[product, ind] = max(prod(slide(:, n:end)));

[Wasi von Deutschland]

If that's the code it gives value for arguments ([1,2,2,1,3,1],3) product=16, ind=1 which is incorrect value should have been 6 and 3 respectively

function [product,ind] = max_product(v,n)
slide = toeplitz(v, v(1:n));
[product, ind] = max(prod(slide(:, n:end)));
end

[Guillaume]

For some reason, I'd inverted the order of the arguments to toeplitz.

Now fixed.

[Stephen23]

+1 nice solution

Answer 3

[Andrei Bobrov]

max_product = @(A,n)max(exp(conv2(log(A(:)),ones(n,1),'valid')));

use:

>> [value,ii] = max_product([1 2 3 4 5 6 7 8 9 10], 2)
value =
    90
ii =
     9
>>

or with function hankel:

max_prod_hankel = @(A,n)max(prod(hankel(A(1:n),A(n:end))));

use:

>> [v,ii] = max_prod_hankel([1 2 3 4 5 6 7 8 9 10], 2)
v =
    90
ii =
     9
>>

[Stephen23]

+1 for the hankel solution

[Andrei Bobrov]

Thank you Stephen.