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[1D] Improve finite-difference Jacobian

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Preserve the sign of elements of the solution vector when perturbing them in
order to avoid triggering discontinuous behavior as the cross zero (which is
caused by the way rate evaluation is handled for negative species
concentrations).
This commit is contained in:
Ray Speth 2016-02-13 18:24:03 -05:00
parent d76704912b
commit 011c9cb6c3
1 changed files with 6 additions and 2 deletions
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8
src/oneD/MultiJac.cpp
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@ -56,9 +56,13 @@ void MultiJac::eval(doublereal* x0, doublereal* resid0, doublereal rdt)
for (j = 0; j < m_points; j++) {
nv = m_resid->nVars(j);
for (n = 0; n < nv; n++) {
// perturb x(n)
// perturb x(n); preserve sign(x(n))
xsave = x0[ipt];
dx = m_atol + fabs(xsave)*m_rtol;
if (xsave >= 0) {
dx = xsave*m_rtol + m_atol;
} else {
dx = xsave*m_rtol - m_atol;
}
x0[ipt] = xsave + dx;
dx = x0[ipt] - xsave;
rdx = 1.0/dx;