Conjugate direction (source code)

= Conjugate direction
{title2=$p_i^TAp_j=0\quad(i\ne j)$}

= A-conjugate direction
{c}
{synonym}

Nonzero <vectors> are conjugate directions with respect to a <symmetric positive-definite matrix> $A$ when they are pairwise <orthogonal> in the <inner product> $\langle u,v\rangle_A=u^TAv$. They need not be <orthogonal> in the ordinary Euclidean <inner product>. They are <linearly independent>: multiplying a vanishing <linear combination> by $p_j^TA$ isolates its $j$th coefficient times $p_j^TAp_j>0$.