How to find the largest product?
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Hi, I am trying to solve this homework. could anyone please help me to solve this?
* Write a function max_product that takes v a vector and n, a positive integer, as inputs and computes the largest product of n consecutive elements of v. It returns the product and the index of the element of v that is the first term of the product. If there are multiple such products in v, the function must return the one with the smallest starting index. As an example, the following call >> [product, ind] = max_product([1 2 2 1 3 1],3); will assign 6 to product and 3 to ind since the max 3-term product in the input vector is 2*1*3. If v has fewer than n elements, the function returns 0 and -1, respectively.
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回答(3 个)
Stephen23
2017-11-21
编辑:Stephen23
2017-11-21
function [product,ind] = max_product(a,n)
product = 0;
ind = -1;
num = numel(a);
for k = 1:1+num-n
tmp = prod(a(k:k+n-1));
if tmp>product
product = tmp;
ind = k;
end
end
end
And tested:
>> [product, ind] = max_product([1 2 2 1 3 1],3)
product = 6
ind = 3
>> [product, ind] = max_product([1 2 2 1 3 9],3)
product = 27
ind = 4
>> [product, ind] = max_product([1 2 2 1 3 9],9)
product = 0
ind = -1
This could be vectorized, or you could use movprod, but using a loop makes the algorithm clear.
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Jan
2017-11-21
编辑:Jan
2017-11-21
And a vectorized version:
function [P, Ind] = max_product(v, n)
X = v((1:numel(v) - n + 1) + (0:n-1).');
[P, Ind] = max(prod(X, 1));
end
6 个评论
silvia a
2018-7-30
编辑:silvia a
2018-7-30
thank you very much for your answer; I have solved it;
I do not know if you guys read these reviews. But I wanted to tell you that your answers and code examples help very much. I am very new to this but trying out your examples really helped me to get started and have a better grasp of things. Thank you!
Andrei Bobrov
2017-11-21
编辑:Andrei Bobrov
2017-11-21
Op! Everyone solves someone else's homework ... I also want! :)
[product1, ind] = max(prod(hankel(a(1:end-b+1),a(end-b+1:end)),2))
as function:
function [product1,ind]=max_product(a,b)
try
[product1, ind] = max(prod(hankel(a(1:end-b+1),a(end-b+1:end)),2));
catch
product1 = 0;
ind = -1;
end
end
with conv2:
function [product1,ind]=max_product(a,b)
try
[product1, ind] = max(exp(conv2(log(a(:)),ones(b,1),'valid')));
catch
product1 = 0;
ind = -1;
end
end
with movsum
[product1, ind] = max(exp(movsum(log(a),[0, b-1])));
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