V
V
Vyacheslav Ovchinnikov2012-06-27 09:44:28
Programming
Vyacheslav Ovchinnikov, 2012-06-27 09:44:28

Does the problem have a solution?

There are two sequences of numbers:
a1, a2, a3… an
b1, b2,b3… bn
The arithmetic mean of these two sequences are equal.
The difference between the sequences is calculated as follows:
R = |a1-b1| + |a2-b2| + |a3-b3| +… + |an-bn|
The problem is whether it is possible to find such a coefficient k by multiplying the first sequence by which
so that the difference between the sequences is minimal.
those.
R = |k*a1-b1| + |k*a2-b2| + |k*a3-b3| +… + |k*an-bn|
those. we need to find a k such that R is minimal.
In other words, you need to choose such a scaling factor for the first sequence so that the difference between the sequences is minimal.
Of course, this problem is quite easily solved by "binary search" (up to a certain accuracy), but for this you need to perform a certain number of calculations R with different k.
Is it possible to somehow find this k not by enumeration?
UPD. All numbers >= 0

Answer the question

In order to leave comments, you need to log in

3 answer(s)
A
AndreyDaeron, 2012-06-27
@ova777

1. R = a1*|k-b1/a1| + a2*|k-b2/a2| + a3|k3-b3/a3| +… + an|k-bn/an| (if ai=0, then we don’t take it out of the brackets and we don’t care.
2. Obviously, such a function is piecewise linear with respect to k on each of the sections, k, for which the modules open with the same sign (assume that a1/b1>b2 /a2>...bn/an, if this is not the case, sort it so that it is.) This means that on the section [(ai/bi,(ai+1)/(bi+1)] the function will be linear (! !!This is generally not true for (-inf,+inf) 3.
Since it is linear, its minimum will be reached at one of the points ai/bi.
bi)
5. Profit
And no binary search ))

S
Salavat Sitdikov, 2012-06-27
@zona7o

I may be wrong, but if the sequences do not have any functional dependency, then no, the only solution is brute force.

T
TheHorse, 2012-06-27
@TheHorse

Binary search needs R(k) to be linear, and in your case, if I'm not mistaken, it can be anything.

Didn't find what you were looking for?

Ask your question

Ask a Question

731 491 924 answers to any question