What is the gradient of $\theta^T X^TX \theta$ ?
The text book says the gradient is $2\theta^TX^TX$,
From this link, I got answer $2X^TX \theta$.
This two answers might be the same, if the matrix is a Symmetric matrix that $2X^TX\theta = 2(\theta^TX^TX)^T$
But how do we prove this? Thank you.
