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updated notes

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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
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Nikolaj Bjorner 2022-12-25 15:28:34 -08:00
parent be5b6f2839
commit 4c6499f28b
1 changed files with 9 additions and 4 deletions
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13
src/math/polysat/saturation.cpp
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@ -1308,7 +1308,7 @@ namespace polysat {
* x >= x*y + x - 1 = (y + 1)*x - 1
* A_x : 1 <= x < 2^128 (A_x is the "allowed" range for x, F_x, the forbidden range is the complement)
* Compute largest infeasible interval on y
* => F_y = [2, 2^128+1[
* => F_y = [2, 2^128 + 1[
*
* starting point y0 := 454
*
@ -1324,7 +1324,7 @@ namespace polysat {
* for every x in A_x : 0 < r(x, y0) = x*y0 - 1 < N
* find F_y, maximal such that
* for every x in A_x, for every y in F_y : 0 < r(x,y), 0 <= p(x,y) < N, 0 <= q(x,y) < N
* for every x in A_x, for every y in F_y : 0 < r(x,y) < N, 0 <= p(x,y) < N, 0 <= q(x,y) < N
*
* Use the fact that the coefficiens to x, y in p, q, r are non-negative
* Note: There isn't ereally anything as negative coefficients because they are already normalized mod N.
@ -1337,14 +1337,19 @@ namespace polysat {
* max y. r(x,y) < N forall x in A_x
* = max y . r(x_max,y) < N, where x_max = 2^128-1
* = max y . y*x_max - 1 <= N - 1
* = floor(N - 1 / x_max) + 1
* = floor(N / x_max)
* = 2^128
*
* max y . q(x, y) < N
* = max y . (y + 1) * x_max - 1 <= N -1
* = floor(N / x_max) - 1
* = 2^128 - 1 (NSB: this is a weaker bound than what it should be. Is using "floor" too much?)
*
* min y . 0 < r(x,y) forall x in A_x
* = min y . 0 < r(x_min, y)
* = min y . 1 <= y*x_min - 1
* = ceil(2 / x_min)
* = 2
* = 2
*
* we have now computed a range around y0 where x >= x*y + x - 1 is false for every x in A_x
* The range is a "forbidden interval" for y and is implied. It is much stronger than resolving on y0.