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slight optimisation of the quadratic interpolation

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Antonin Portelli 2015-12-02 18:10:10 +00:00
parent e950e18639
commit ff968efd94
1 changed files with 10 additions and 11 deletions
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21
lib/TabFunction.cpp
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@ -92,7 +92,7 @@ double TabFunction::operator()(const double *arg) const
break;
}
case InterpType::QUADRATIC: {
double xs[3], ys[3], as[3];
double xs[3], ys[3], ds[3], d01, d02, d12;
auto it = nearest(x);
if (it == value_.begin()) {
it = next(it);
@ -106,18 +106,17 @@ double TabFunction::operator()(const double *arg) const
ys[1] = it->second;
xs[2] = next(it)->first;
ys[2] = next(it)->second;
ds[0] = x - xs[0];
ds[1] = x - xs[1];
ds[2] = x - xs[2];
d01 = xs[0] - xs[1];
d02 = xs[0] - xs[2];
d12 = xs[1] - xs[2];
// Lagrange polynomial coefficient computation
as[0]
= (x - xs[1]) / (xs[0] - xs[1])
* (x - xs[2]) / (xs[0] - xs[2]);
as[1]
= (x - xs[0]) / (xs[1] - xs[0])
* (x - xs[2]) / (xs[1] - xs[2]);
as[2]
= (x - xs[0]) / (xs[2] - xs[0])
* (x - xs[1]) / (xs[2] - xs[1]);
result = as[0] * ys[0] + as[1] * ys[1] + as[2] * ys[2];
result = ds[1]/d01*ds[2]/d02*ys[0]
-ds[0]/d01*ds[2]/d12*ys[1]
+ds[0]/d02*ds[1]/d12*ys[2];
break;
}
default: