diff --git a/include/hpp/spline/CMakeLists.txt b/include/hpp/spline/CMakeLists.txt
index b417e3d2cbfec4e0f3955998bd44a9d3fb09e0dc..05c00ac1dd969ac6f011b7d1ff4a67d33e3c936a 100644
--- a/include/hpp/spline/CMakeLists.txt
+++ b/include/hpp/spline/CMakeLists.txt
@@ -10,6 +10,7 @@ SET(${PROJECT_NAME}_HEADERS
cubic_spline.h
curve_constraint.h
quintic_spline.h
+ linear_variable.h
)
INSTALL(FILES
diff --git a/include/hpp/spline/linear_variable.h b/include/hpp/spline/linear_variable.h
new file mode 100644
index 0000000000000000000000000000000000000000..3afe4ba01058cd0fcd7180da0abeedfe3e2d0d3c
--- /dev/null
+++ b/include/hpp/spline/linear_variable.h
@@ -0,0 +1,201 @@
+/**
+* \file linear_variable.h
+* \brief storage for variable points of the form p_i = a_i x + b_i
+* \author Steve T.
+* \version 0.1
+* \date 07/02/2019
+*/
+
+
+#ifndef _CLASS_LINEAR_VARIABLE
+#define _CLASS_LINEAR_VARIABLE
+
+#include "curve_abc.h"
+
+#include "MathDefs.h"
+
+#include <math.h>
+#include <vector>
+#include <Eigen/Core>
+#include <stdexcept>
+
+namespace spline
+{
+template <int Dim, typename Numeric=double>
+struct linear_variable{
+ typedef Numeric num_t;
+ typedef Eigen::Matrix<num_t, Dim, Dim> matrix_t;
+ typedef Eigen::Matrix<num_t, Dim, 1> point_t;
+
+ typedef linear_variable<Dim, Numeric> linear_variable_t;
+
+ matrix_t A_;
+ point_t b_;
+
+ linear_variable(): A_(matrix_t::Identity()), b_(point_t::Zero()){}
+ linear_variable(const matrix_t& A, const point_t& b):A_(A),b_(b) {}
+ linear_variable(const point_t& b):A_(matrix_t::Zero()),b_(b) {} // constant
+
+
+ linear_variable& operator+=(const linear_variable& w1)
+ {
+ this->A_ += w1.A_;
+ this->b_ += w1.b_;
+ return *this;
+ }
+ linear_variable& operator-=(const linear_variable& w1)
+ {
+ this->A_ -= w1.A_;
+ this->b_ -= w1.b_;
+ return *this;
+ }
+
+ static linear_variable_t Zero(size_t dim=0){
+ linear_variable_t w;
+ w.A_ = matrix_t::Zero();
+ w.b_ = point_t::Zero();
+ return w;
+ }
+};
+
+
+template<typename Var>
+struct variables{
+ typedef Var var_t;
+ typedef variables<Var> variables_t;
+
+ typedef std::vector<var_t> T_var_t;
+ typedef typename T_var_t::iterator IT_var_t;
+ typedef typename T_var_t::const_iterator CIT_var_t;
+
+ T_var_t variables_;
+
+ variables() {}
+
+ variables& operator+=(const variables& w1)
+ {
+ if(variables_.size() == 0)
+ variables_ = w1.variables_;
+ else if (w1.variables_.size() !=0)
+ {
+ assert(variables_.size() == w1.variables_.size());
+ CIT_var_t cit = w1.variables_.begin();
+ for(IT_var_t it = variables_.begin(); it != variables_.end(); ++it, ++cit)
+ (*it)+=(*cit);
+ }
+ return *this;
+ }
+
+ variables& operator-=(const variables& w1)
+ {
+ if(variables_.size() == 0)
+ variables_ = w1.variables_;
+ else if (w1.variables_.size() !=0)
+ {
+ assert(variables_.size() == w1.variables_.size());
+ CIT_var_t cit = w1.variables_.begin();
+ for(IT_var_t it = variables_.begin(); it != variables_.end(); ++it, ++cit)
+ (*it)-=(*cit);
+ }
+ return *this;
+ }
+
+ static variables_t Zero(size_t /*dim*/){
+ variables_t w;
+ return w;
+ }
+};
+
+template <int D, typename N>
+inline linear_variable<D,N> operator+(const linear_variable<D,N>& w1, const linear_variable<D,N>& w2)
+{
+ return linear_variable<D,N>(w1.A_ + w2.A_, w1.b_ + w2.b_);
+}
+
+template <int D, typename N>
+linear_variable<D,N> operator-(const linear_variable<D,N>& w1, const linear_variable<D,N>& w2)
+{
+ return linear_variable<D,N>(w1.A_ - w2.A_, w1.b_ - w2.b_);
+}
+
+template <int D, typename N>
+linear_variable<D,N> operator*(const double k, const linear_variable<D,N>& w){
+ return linear_variable<D,N>(k*w.A_,k*w.b_);
+}
+
+template <int D, typename N>
+linear_variable<D,N> operator*(const linear_variable<D,N>& w,const double k){
+ return linear_variable<D,N>(k*w.A_,k*w.b_);
+}
+
+template <int D, typename N>
+linear_variable<D,N> operator/(const linear_variable<D,N>& w,const double k){
+ return linear_variable<D,N>(w.A_/k,w.b_/k);
+}
+
+template<typename V>
+variables<V> operator+(const variables<V>& w1, const variables<V>& w2)
+{
+ if(w2.variables_.size() == 0)
+ return w1;
+ if(w1.variables_.size() == 0)
+ return w2;
+ variables<V> res;
+ assert(w2.variables_.size() == w1.variables_.size());
+ typename variables<V>::CIT_var_t cit = w1.variables_.begin();
+ for(typename variables<V>::CIT_var_t cit2 = w2.variables_.begin(); cit2 != w2.variables_.end(); ++cit, ++cit2)
+ res.variables_.push_back((*cit)+(*cit2));
+ return res;
+}
+
+template<typename V>
+variables<V> operator-(const variables<V>& w1, const variables<V>& w2)
+{
+ if(w2.variables_.size() == 0)
+ return w1;
+ if(w1.variables_.size() == 0)
+ return w2;
+ variables<V> res;
+ assert(w2.variables_.size() == w1.variables_.size());
+ typename variables<V>::CIT_var_t cit = w1.variables_.begin();
+ for(typename variables<V>::CIT_var_t cit2 = w2.variables_.begin(); cit2 != w2.variables_.end(); ++cit, ++cit2)
+ res.variables_.push_back((*cit)-(*cit2));
+ return res;
+}
+
+template<typename V>
+variables<V> operator*(const double k, const variables<V>& w)
+{
+ if(w.variables_.size() == 0)
+ return w;
+ variables<V> res;
+ for(typename variables<V>::CIT_var_t cit = w.variables_.begin(); cit != w.variables_.end(); ++cit)
+ res.variables_.push_back(k*(*cit));
+ return res;
+}
+
+template<typename V>
+variables<V> operator*(const variables<V>& w,const double k)
+{
+ if(w.variables_.size() == 0)
+ return w;
+ variables<V> res;
+ for(typename variables<V>::CIT_var_t cit = w.variables_.begin(); cit != w.variables_.end(); ++cit)
+ res.variables_.push_back((*cit)*k);
+ return res;
+}
+
+template<typename V>
+variables<V> operator/(const variables<V>& w,const double k)
+{
+ if(w.variables_.size() == 0)
+ return w;
+ variables<V> res;
+ for(typename variables<V>::CIT_var_t cit = w.variables_.begin(); cit != w.variables_.end(); ++cit)
+ res.variables_.push_back((*cit)/k);
+ return res;
+}
+
+} // namespace spline
+#endif //_CLASS_LINEAR_VARIABLE
+