On the space $\mathbb{C}^n$ we define the scalar product: $\langle x,y\rangle = \sum_{i=1}^n x_i y ̅_i $ , now we define the operator: $[\space ,\space ]: \mathbb{C}^n\times \mathbb{C}^n\to\mathbb{C} $ as $[x,y]= \langle Ax,y\rangle$ when $A$ is an invertible complex matrix.
Which condition should be required for $A$ to have complex conjugate : $[y,x]= \overline{[x,y]}$ ?
Assuming that $A$ satisfies the condition of Section 1, which condition should be required for $A$ to have positivity: $[x,x]=0\iff x=0,[x,x]\geq 0 $?
For finding these conditions, I need to use the inner product rules:
(a) $\langle x,y\rangle =\overline{\langle y,x\rangle}$ (the bar denotes the complex conjugate)
(b) $\langle αx +βy, z\rangle =α\langle x, z\rangle + β\langle y, z\rangle $
(c) $\langle x,x\rangle \geq 0 $
(d) $\langle x,x\rangle = 0 $ implies x = 0.
I've already managed to prove linearity of the product easily.
(homework)tag: it should never be added without explicit acknowledgement by the OP that the question is homework. – Brian M. Scott Feb 11 at 7:37