Problems with taking magnitude

[jeanluct]

Some problems with taking magnitudes: if I have a mathvector of complex numbers, then the magnitude should return a real, not complex, number. Also, it shouldn't be defined as x*x, as this is wrong for complex numbers. Need to call a magnitude function for the type. Maybe also need a magnitude type. Define with traits?

[jeanluct]

See issue #5.

[jeanluct]

Part of the problem is with

template<class T, class S = T>
class mathvector : public vector<T> // note that this is jlt::vector

S = T is not the right default for complex.

[jeanluct]

See mathvector_test.cpp. The situation is better: mathvector<complex> now makes a vector with complex scalar type, so mag2 returns a complex (with zero real part). mathvector<complex,double> is the more sensible case.