320 lines
8.4 KiB
C++
320 lines
8.4 KiB
C++
/* dynamo:- Event driven molecular dynamics simulator
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http://www.marcusbannerman.co.uk/dynamo
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Copyright (C) 2011 Marcus N Campbell Bannerman <m.bannerman@gmail.com>
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This program is free software: you can redistribute it and/or
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modify it under the terms of the GNU General Public License
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version 3 as published by the Free Software Foundation.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#pragma once
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#include <boost/numeric/ublas/vector.hpp>
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#include <boost/numeric/ublas/vector_proxy.hpp>
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#include <boost/numeric/ublas/matrix.hpp>
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#include <boost/numeric/ublas/triangular.hpp>
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#include <boost/numeric/ublas/lu.hpp>
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#include <exception>
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namespace ublas = boost::numeric::ublas;
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class Spline : private std::vector<std::pair<double, double> >
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{
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public:
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//The boundary conditions available
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enum BC_type {
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FIXED_1ST_DERIV_BC,
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FIXED_2ND_DERIV_BC,
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PARABOLIC_RUNOUT_BC
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};
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enum Spline_type {
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LINEAR,
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CUBIC
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};
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//Constructor takes the boundary conditions as arguments, this
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//sets the first derivative (gradient) at the lower and upper
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//end points
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Spline():
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_valid(false),
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_BCLow(FIXED_2ND_DERIV_BC), _BCHigh(FIXED_2ND_DERIV_BC),
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_BCLowVal(0), _BCHighVal(0),
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_type(CUBIC)
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{}
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typedef std::vector<std::pair<double, double> > base;
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typedef base::const_iterator const_iterator;
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//Standard STL read-only container stuff
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const_iterator begin() const { return base::begin(); }
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const_iterator end() const { return base::end(); }
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void clear() { _valid = false; base::clear(); _data.clear(); }
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size_t size() const { return base::size(); }
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size_t max_size() const { return base::max_size(); }
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size_t capacity() const { return base::capacity(); }
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bool empty() const { return base::empty(); }
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//Add a point to the spline, and invalidate it so its
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//recalculated on the next access
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inline void addPoint(double x, double y)
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{
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_valid = false;
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base::push_back(std::pair<double, double>(x,y));
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}
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//Reset the boundary conditions
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inline void setLowBC(BC_type BC, double val = 0)
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{ _BCLow = BC; _BCLowVal = val; _valid = false; }
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inline void setHighBC(BC_type BC, double val = 0)
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{ _BCHigh = BC; _BCHighVal = val; _valid = false; }
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void setType(Spline_type type) { _type = type; _valid = false; }
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//Check if the spline has been calculated, then generate the
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//spline interpolated value
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double operator()(double xval)
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{
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if (!_valid) generate();
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//Special cases when we're outside the range of the spline points
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if (xval <= x(0)) return lowCalc(xval);
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if (xval >= x(size()-1)) return highCalc(xval);
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//Check all intervals except the last one
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for (std::vector<SplineData>::const_iterator iPtr = _data.begin();
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iPtr != _data.end()-1; ++iPtr)
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if ((xval >= iPtr->x) && (xval <= (iPtr+1)->x))
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return splineCalc(iPtr, xval);
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return splineCalc(_data.end() - 1, xval);
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}
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private:
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///////PRIVATE DATA MEMBERS
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struct SplineData { double x,a,b,c,d; };
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//vector of calculated spline data
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std::vector<SplineData> _data;
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//Second derivative at each point
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ublas::vector<double> _ddy;
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//Tracks whether the spline parameters have been calculated for
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//the current set of points
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bool _valid;
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//The boundary conditions
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BC_type _BCLow, _BCHigh;
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//The values of the boundary conditions
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double _BCLowVal, _BCHighVal;
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Spline_type _type;
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///////PRIVATE FUNCTIONS
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//Function to calculate the value of a given spline at a point xval
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inline double splineCalc(std::vector<SplineData>::const_iterator i, double xval)
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{
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const double lx = xval - i->x;
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return ((i->a * lx + i->b) * lx + i->c) * lx + i->d;
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}
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inline double lowCalc(double xval)
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{
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const double lx = xval - x(0);
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if (_type == LINEAR)
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return lx * _BCHighVal + y(0);
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const double firstDeriv = (y(1) - y(0)) / h(0) - 2 * h(0) * (_data[0].b + 2 * _data[1].b) / 6;
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switch(_BCLow)
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{
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case FIXED_1ST_DERIV_BC:
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return lx * _BCLowVal + y(0);
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case FIXED_2ND_DERIV_BC:
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return lx * lx * _BCLowVal + firstDeriv * lx + y(0);
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case PARABOLIC_RUNOUT_BC:
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return lx * lx * _ddy[0] + lx * firstDeriv + y(0);
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}
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throw std::runtime_error("Unknown BC");
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}
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inline double highCalc(double xval)
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{
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const double lx = xval - x(size() - 1);
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if (_type == LINEAR)
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return lx * _BCHighVal + y(size() - 1);
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const double firstDeriv = 2 * h(size() - 2) * (_ddy[size() - 2] + 2 * _ddy[size() - 1]) / 6 + (y(size() - 1) - y(size() - 2)) / h(size() - 2);
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switch(_BCHigh)
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{
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case FIXED_1ST_DERIV_BC:
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return lx * _BCHighVal + y(size() - 1);
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case FIXED_2ND_DERIV_BC:
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return lx * lx * _BCHighVal + firstDeriv * lx + y(size() - 1);
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case PARABOLIC_RUNOUT_BC:
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return lx * lx * _ddy[size()-1] + lx * firstDeriv + y(size() - 1);
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}
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throw std::runtime_error("Unknown BC");
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}
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//These just provide access to the point data in a clean way
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inline double x(size_t i) const { return operator[](i).first; }
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inline double y(size_t i) const { return operator[](i).second; }
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inline double h(size_t i) const { return x(i+1) - x(i); }
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//Invert a arbitrary matrix using the boost ublas library
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template<class T>
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bool InvertMatrix(ublas::matrix<T> A,
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ublas::matrix<T>& inverse)
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{
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using namespace ublas;
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// create a permutation matrix for the LU-factorization
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permutation_matrix<std::size_t> pm(A.size1());
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// perform LU-factorization
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int res = lu_factorize(A,pm);
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if( res != 0 ) return false;
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// create identity matrix of "inverse"
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inverse.assign(ublas::identity_matrix<T>(A.size1()));
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// backsubstitute to get the inverse
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lu_substitute(A, pm, inverse);
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return true;
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}
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//This function will recalculate the spline parameters and store
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//them in _data, ready for spline interpolation
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void generate()
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{
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if (size() < 2)
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throw std::runtime_error("Spline requires at least 2 points");
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//If any spline points are at the same x location, we have to
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//just slightly seperate them
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{
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bool testPassed(false);
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while (!testPassed)
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{
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testPassed = true;
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std::sort(base::begin(), base::end());
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for (base::iterator iPtr = base::begin(); iPtr != base::end() - 1; ++iPtr)
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if (iPtr->first == (iPtr+1)->first)
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{
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if ((iPtr+1)->first != 0)
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(iPtr+1)->first += (iPtr+1)->first
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* std::numeric_limits<double>::epsilon() * 10;
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else
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(iPtr+1)->first = std::numeric_limits<double>::epsilon() * 10;
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testPassed = false;
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break;
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}
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}
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}
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const size_t e = size() - 1;
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switch (_type)
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{
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case LINEAR:
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{
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_data.resize(e);
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for (size_t i(0); i < e; ++i)
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{
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_data[i].x = x(i);
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_data[i].a = 0;
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_data[i].b = 0;
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_data[i].c = (y(i+1) - y(i)) / (x(i+1) - x(i));
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_data[i].d = y(i);
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}
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break;
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}
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case CUBIC:
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{
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ublas::matrix<double> A(size(), size());
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for (size_t yv(0); yv <= e; ++yv)
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for (size_t xv(0); xv <= e; ++xv)
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A(xv,yv) = 0;
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for (size_t i(1); i < e; ++i)
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{
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A(i-1,i) = h(i-1);
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A(i,i) = 2 * (h(i-1) + h(i));
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A(i+1,i) = h(i);
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}
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ublas::vector<double> C(size());
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for (size_t xv(0); xv <= e; ++xv)
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C(xv) = 0;
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for (size_t i(1); i < e; ++i)
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C(i) = 6 *
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((y(i+1) - y(i)) / h(i)
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- (y(i) - y(i-1)) / h(i-1));
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//Boundary conditions
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switch(_BCLow)
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{
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case FIXED_1ST_DERIV_BC:
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C(0) = 6 * ((y(1) - y(0)) / h(0) - _BCLowVal);
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A(0,0) = 2 * h(0);
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A(1,0) = h(0);
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break;
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case FIXED_2ND_DERIV_BC:
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C(0) = _BCLowVal;
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A(0,0) = 1;
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break;
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case PARABOLIC_RUNOUT_BC:
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C(0) = 0; A(0,0) = 1; A(1,0) = -1;
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break;
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}
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switch(_BCHigh)
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{
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case FIXED_1ST_DERIV_BC:
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C(e) = 6 * (_BCHighVal - (y(e) - y(e-1)) / h(e-1));
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A(e,e) = 2 * h(e - 1);
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A(e-1,e) = h(e - 1);
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break;
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case FIXED_2ND_DERIV_BC:
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C(e) = _BCHighVal;
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A(e,e) = 1;
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break;
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case PARABOLIC_RUNOUT_BC:
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C(e) = 0; A(e,e) = 1; A(e-1,e) = -1;
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break;
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}
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ublas::matrix<double> AInv(size(), size());
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InvertMatrix(A,AInv);
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_ddy = ublas::prod(C, AInv);
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_data.resize(size()-1);
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for (size_t i(0); i < e; ++i)
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{
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_data[i].x = x(i);
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_data[i].a = (_ddy(i+1) - _ddy(i)) / (6 * h(i));
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_data[i].b = _ddy(i) / 2;
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_data[i].c = (y(i+1) - y(i)) / h(i) - _ddy(i+1) * h(i) / 6 - _ddy(i) * h(i) / 3;
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_data[i].d = y(i);
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}
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}
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}
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_valid = true;
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}
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};
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