Sunday, May 21, 2006
SF: Latest still won't work well
So I went ahead and thought more carefully about my latest surrogate factoring equations, and realized why they couldn't work well.
I figured out that to get solutions you needed with
f_1 f_2 = k_2 z^2
and
g_1 g_2 = k_2 z^2 + T
for f_1 + f_2 = g_1 + g_2,
with all the variables rationals, and I chased down that angle and determined that you need to pick k_2 z^2 perfectly, and the odds are slim. So those equations won't work well.
I did notice something weird though, as if you have, with some variable changes for simplicity,
f_1 f_2 = k
and
g_1 g_2 = k + M
with f_1 + f_2 = g_1 + g_2,
it's trival to show that requires that
(2f_1 g_1 - (f_1^2 + k))^2 = (f_1^2 - (k + 2M))^2 - 4M(k + M)
so I thought maybe you could let k be your target, and search for an M that will work to give a rational f_1, but maybe I did some of the algebra wrong as I tried a simple example:
k = 15, M=1
and that gives f_1 = 9, as a possible, which is close, but it'd be nicer if it were f_1 = 3.
In any event, it looks like another failure for the surrogate factoring idea.
The equations could factor, but only if you picked k_2 z^2 precisely and the odds of getting them right are long--unless you already have T factored, so, another failure.
I figured out that to get solutions you needed with
f_1 f_2 = k_2 z^2
and
g_1 g_2 = k_2 z^2 + T
for f_1 + f_2 = g_1 + g_2,
with all the variables rationals, and I chased down that angle and determined that you need to pick k_2 z^2 perfectly, and the odds are slim. So those equations won't work well.
I did notice something weird though, as if you have, with some variable changes for simplicity,
f_1 f_2 = k
and
g_1 g_2 = k + M
with f_1 + f_2 = g_1 + g_2,
it's trival to show that requires that
(2f_1 g_1 - (f_1^2 + k))^2 = (f_1^2 - (k + 2M))^2 - 4M(k + M)
so I thought maybe you could let k be your target, and search for an M that will work to give a rational f_1, but maybe I did some of the algebra wrong as I tried a simple example:
k = 15, M=1
and that gives f_1 = 9, as a possible, which is close, but it'd be nicer if it were f_1 = 3.
In any event, it looks like another failure for the surrogate factoring idea.
The equations could factor, but only if you picked k_2 z^2 precisely and the odds of getting them right are long--unless you already have T factored, so, another failure.