S-expression: Difference between revisions

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m Sk (square-particulars): linked table where relevant
Godtone (talk | contribs)
m Mathematical derivation: re-structuring slightly for clarity and for next section
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= (k<sup>3</sup> + 3k<sup>2</sup>)/( k<sup>3</sup> + 3k<sup>2</sup> - 4 )
= (k<sup>3</sup> + 3k<sup>2</sup>)/( k<sup>3</sup> + 3k<sup>2</sup> - 4 )


Note that when k = 2n, everything in the numerator and denominator is divisible by 4 because the only instances of k have it raised to a power of 2 or greater meaning there will be a factor of (2n)<sup>2</sup> = 4n<sup>2</sup>, therefore Sk/S(k+2) is superparticular when k is even.
This result will be useful, so we will refer to it as [Eq. 1]:


When k = 4n+1, we have to do some work to show it is superparticular:
'''[Eq. 1]'''  Sk/S(k+2) = (k<sup>3</sup> + 3k<sup>2</sup>)/( k<sup>3</sup> + 3k<sup>2</sup> - 4 )


First let's note (4n+1)<sup>3</sup> = (4n+1)(4n+1)(4n+1) = (4n)<sup>3</sup> + 3*4(4n)<sup>2</sup> + 3*(4n)<sup>2</sup> + 1 is of the form 4m+1.
Note that when k = 2n in [Eq. 1], everything in the numerator and denominator is divisible by 4 because the only instances of k have it raised to a power of 2 or greater meaning there will be a factor of (2n)<sup>2</sup> = 4n<sup>2</sup>, therefore Sk/S(k+2) is superparticular when k is even.


Next let's note (4n+1)<sup>2</sup> = (4n)<sup>2</sup> + 4(4n) + 1 is also of the form 4m+1.
When k = 4n+1 in [Eq. 1], we have to do some work to show the result is superparticular:


Therefore we can replace their occurrences with 4m+1 and 4a+1 respectively, without having to worry about what m and a are (as we know they are positive integers).
(4n+1)<sup>3</sup> = (4n)<sup>3</sup> + 3*(4n)<sup>2</sup> + 3*4n + 1 is of the form 4m+1.
 
(4n+1)<sup>2</sup> = (4n)<sup>2</sup> + 2*4n + 1 is also of the form 4m+1.
 
Therefore we can replace their occurrences in [Eq. 1] with 4m+1 and 4a+1 respectively, without having to worry about what m and a are (as we only need to know that m and a are positive integers). Therefore to show S(4n+1)/S(4n+3) is superparticular, we plug in k=4n+1 into [Eq. 1] and then do the replacements and simplify to a superparticular, shown below:


S(4n+1)/S(4n+3) = ( (4n+1)<sup>3</sup> + 3(4n+1)<sup>2</sup> )/( (4n+1)<sup>3</sup> + 3(4n+1)<sup>2</sup> - 4 )
S(4n+1)/S(4n+3) = ( (4n+1)<sup>3</sup> + 3(4n+1)<sup>2</sup> )/( (4n+1)<sup>3</sup> + 3(4n+1)<sup>2</sup> - 4 )