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bug fix in shift_var

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Signed-off-by: Lev Nachmanson <levnach@hotmail.com>
This commit is contained in:
Lev Nachmanson 2020-02-14 16:59:31 -08:00
parent 99b71a9f9e
commit b5276e93bb
1 changed files with 18 additions and 8 deletions
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26
src/math/lp/int_solver.cpp
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@ -513,15 +513,25 @@ bool int_solver::shift_var(unsigned j, unsigned range) {
}
SASSERT(!inf_l && !inf_u);
mpq r = floor((u - l) / m);
if (r < mpq(range)) range = static_cast<unsigned>(r.get_uint64());
// the interval contains at least range multiples of m.
// the number of multiples to the left of the value of j is floor((get_value(j) - l.x)/m)
// shift either left or right of the current value by available multiples.
impq shift = impq(random() % (range + 1)) - impq(floor((x - l) / m));
impq new_val = x + m * shift;
// The shift has to be a multiple of m: let us look for s, such that the shift is m*s.
// We have new_val = x+m*s <= u, so m*s <= u-x and, finally, s <= floor((u- x)/m) = a
// The symmetric reasoning gives us s >= ceil((l-x)/m) = b
// We randomly pick s in the segment [b, a]
mpq a = floor((u - x) / m);
mpq b = ceil((l - x) / m);
mpq r = a - b;
if (!r.is_pos())
return false;
TRACE("int_solver", tout << "a = " << a << ", b = " << b << ", r = " << r<< ", m = " << m << "\n";);
if (r < mpq(range))
range = static_cast<unsigned>(r.get_uint64());
mpq s = b + mpq(random() % (range + 1));
impq new_val = x + m * impq(s);
TRACE("int_solver", tout << "new_val = " << new_val << "\n";);
SASSERT(l <= new_val && new_val <= u);
set_value_for_nbasic_column_ignore_old_values(j, new_val); return true;
set_value_for_nbasic_column_ignore_old_values(j, new_val);
return true;
}
bool int_solver::non_basic_columns_are_at_bounds() const {