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Compute the derivative directly (not using epsilon parameter).

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This commit is contained in:
Xavier Raynaud 2012-03-15 16:15:32 +01:00
parent 9c226c1b24
commit 49a53f1935
1 changed files with 9 additions and 6 deletions
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15
opm/core/utility/linearInterpolation.hpp
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@ -74,12 +74,15 @@ namespace Opm
const std::vector<T>& yv,
double x)
{
double epsilon = 1e-4; // @@ Ad hoc, should choose based on xv.
double x_low = std::max(xv[0], x - epsilon);
double x_high = std::min(xv.back(), x + epsilon);
T low = linearInterpolation(xv, yv, x_low);
T high = linearInterpolation(xv, yv, x_high);
return (high - low)/(x_high - x_low);
std::vector<double>::const_iterator lb = std::lower_bound(xv.begin(), xv.end(), x);
int lb_ix = lb - xv.begin();
if (lb_ix == 0) {
return 0.;
} else if (lb_ix == int(xv.size())) {
return 0.;
} else {
return (yv[lb_ix] - yv[lb_ix - 1])/(xv[lb_ix] - xv[lb_ix - 1]);
}
}