Multipliers for series for manipulating signs of the terms

In summary, the conversation discussed techniques for creating infinite series with different orders of signs using multipliers, such as (-1)^n. The speaker has been working on finding different combinations beyond the ones commonly used, and has derived a general solution for any combination of pairs of positive and negative terms. They have also discussed using binary interference and treating the signs as 0's and 1's to find patterns. The speaker asks if these patterns have a specific name or implementation in mathematics.
  • #1
mesa
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There are multipliers that can be used when building infinite series that can create several different orders for the signs of consecutive terms by, for example, (-1)^n to get,

- + - + - +...

but I have been having difficulty figuring out any beyond the following,

+ - + - + -...
+ + - - + +...
+ - - - + - - -...
and,
- + + + - + + +...

What else do we have?
 
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  • #2
mesa said:
There are multipliers that can be used when building infinite series that can create several different orders for the signs of consecutive terms by, for example, (-1)^n to get,

- + - + - +...

but I have been having difficulty figuring out any beyond the following,

you can halve your work by noticing that some are the negative of another
eg:

- + - + - + is (-1)^n
+ - + - + - = -1x(- + - + - +) is -(-1)^n = (-1)^(n+1) = (-1)^(n-1)
 
  • #3
Simon Bridge said:
you can halve your work by noticing that some are the negative of another
eg:

- + - + - + is (-1)^n
+ - + - + - = -1x(- + - + - +) is -(-1)^n = (-1)^(n+1) = (-1)^(n-1)

Yup, we sure can. I suppose adding in my last line on my post was a bit redundant.

The first set can obviously be done with the old standby
(-1)^n to get,
- + - + - +...
and
(-1)^(n+1) or -(-1)^n to get the opposite set,
+ - + - + -...
as you had suggested.

For the - - + + - - + +... I came up with this,
i^(n(n+1))
The negative of course will give + + - - + + - -...

For those last two in my post it took a bit of work to derive but the final form is,
+/- (ni^(n(n+1))+n(-1)^n+1) / ((ni^(n(n+1))+n(-1)^n+1)^2)^(1/2)
to get + - - - + - - - +... and the - + + + - + + + -... depending on the sign

That was a fun solution to get as I used whole numbers to get the sign pattern and then simply divided by the square root of that quantity squared for each term to get back to '1' or '-1'. The '+1' in each term was to eliminate the '0's'

The problem I face now is there are no combinations of these forms that will yield something different. If I can get to say + + + - - - + + +... then that will give some room for manipulation. I have also been working on + - - - + - - - + by trying to eliminate the middle positive so we would instead have + - - - - - - - +... (the negative being just the opposite sign).

What do we currently have in mathematics? Or do you have any techniques of your own?
 
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  • #4
I just finished deriving a 'general solution' for any combination of 'pairs' of positive and negative terms. For example the solution will give,

+++---+++---...

++++----++++----...

+++++-----+++++-----...

++++++------++++++------...
etc. etc.

How exciting!
What does mathematics have available today? It would be fun to compare notes!
 
  • #5
You want to find a way to label the combinations so you can summarize the realtionships.
The ones you've found are periodic functions ... you can also get interference i.e.:

(+++---+++---++++...)x(++++----++++----)=(+++-++--+-------...)
 
  • #6
Simon Bridge said:
You want to find a way to label the combinations so you can summarize the realtionships.
The ones you've found are periodic functions ... you can also get interference i.e.:

(+++---+++---++++...)x(++++----++++----)=(+++-++--+-------...)

Makes sense, always good to stick with the nomenclature.

I have been playing with these quite a bit, there is a wealth of interference patterns that can be produced (infinite) much like your example above but given enough time they all eventually repeat their patterns.

The last thing to find (for now) is a pattern that does not repeat but grows at a steady rate with time, e.g.

-++---++++-----++++++...
or
-++-+++-++++-+++++-++++++...

With this last tool building infinite series will become substantially easier (albeit they are still tricky buggers!). These are periodic but change with time, what would the proper 'label' for functions of this type? Periodic expansive functions?

I haven't even began to think about how to do this and school starts tomorrow :P
...although it's been a wonderfully productive break!
 
  • #7
You've noticed that ##\cos(n\pi)## gives alternating 1 and -1 and built from there.
You may also like to look at binary interference ... so instead of + and - you have 0 and 1.

In a way you just need to look for functions with the pattern of zeros you need.
i.e. treat either the +'s pr the -'s as a background that you change individual bits of.

It's a very big subject ... i.e. try for this one:

+-+-++-+++-+++++-++++++++-...

or:
-------+------+-------++-----+-------+-+-----++------+++----+---...

or:
+++-+++-++---++-+...

... do you recognize the patterns?
They may be easier to see as strings of 1's and 0's.
 
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  • #8
Simon Bridge said:
You've noticed that ##\cos(n\pi)## gives alternating 1 and -1 and built from there.

A PM I sent you had the function I derived using sin combined with post #3's derivation for ++--++--... and by going 'inside' each period to generate 'general solution' for all 'paired' signs of any number of terms. It seems you are suggesting a different method?

Simon Bridge said:
You may also like to look at binary interference ... so instead of + and - you have 0 and 1.

In a way you just need to look for functions with the pattern of zeros you need.
i.e. treat either the +'s pr the -'s as a background that you change individual bits of.

Taking advantage of the 0's is how I came to that function, neat!

Simon Bridge said:
It's a very big subject ... i.e. try for this one:

+-+-++-+++-+++++-++++++++-...

or:
-------+------+-------++-----+-------+-+-----++------+++----+---...

or:
+++-+++-++---++-+...

... do you recognize the patterns?
They may be easier to see as strings of 1's and 0's.

Do these patterns repeat?
 
  • #9
Do these patterns repeat?
The second one repeats in about 2050 terms, the others two do not.

How about:
++++++++++++-+-+-+-++-+-+++-+-++++...
... repeats after 90 terms.

++-----+---+---+--+----+--++---+-+--...
... repeats after 60 but:

++-+++---+-+++-++++---+--+...
... does not repeat.

Working out generating functions for sequences, even ones with easy algorithms, is pretty tough.
But if you enjoy this sort of thing, you'll probably enjoy cryptography.
 
  • #10
Simon Bridge said:
The second one repeats in about 2050 terms, the others two do not.

Isn't that kind of information important to solving those problems?

Simon Bridge said:
Working out generating functions for sequences, even ones with easy algorithms, is pretty tough.
But if you enjoy this sort of thing, you'll probably enjoy cryptography.

I prefer to generate, for example, my PM on the Basal problem.
 
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  • #11
Isn't that kind of information important to solving those problems?
It can be yes.
(Not providing that information also tells you something about the pattern - it's metadata.)

Even with that information there is more than one generator.

I'll leave you to it.
 
  • #12
Simon Bridge said:
It can be yes.
(Not providing that information also tells you something about the pattern - it's metadata.)

I can appreciate that.

Simon Bridge said:
Even with that information there is more than one generator.

I'll leave you to it.

Fair enough, although I expect to continue our discussion on Basel as well.
 
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1. How do multipliers for series work?

Multipliers for series are mathematical expressions that are used to manipulate the signs of the terms in a series. They can be positive or negative and are typically used to simplify or rearrange series to make them easier to solve.

2. What is the purpose of using multipliers for series?

The purpose of using multipliers for series is to manipulate the signs of the terms in a series in order to simplify it or rearrange it in a way that makes it easier to solve. This can be especially helpful when dealing with complex or lengthy series.

3. How do I know when to use multipliers for series?

Multipliers for series can be used whenever there is a need to manipulate the signs of the terms in a series. This is often seen in mathematical equations or formulas that involve series, but it can also be used in other contexts where series are present.

4. Are there different types of multipliers for series?

Yes, there are different types of multipliers for series. Some of the most common ones include the alternating series multiplier, which alternates between positive and negative values, and the staircase series multiplier, which follows a specific pattern of positive and negative values.

5. Can multipliers for series be used in other mathematical concepts?

Yes, multipliers for series can be applied to other mathematical concepts, such as limits and derivatives. They can also be used in real-life scenarios that involve series, such as in finance or engineering problems.

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