Grad[expr, aVariable]

Aliases: Grad, NEVER USE Gradient

Description: $Grad[expr, aVariable]$ takes the gradient of expression $expr$ with respect to the variable $aVariable$. Quite useful for computations with quadratic Hamiltonians in $H^\infty$ control. BEWARE Gradient calls the Mma gradient and makes a mess.

Arguments: $expr$ is an expression containing $var$. $aVariable$ is a variable.

Comments / Limitations: This only works reliably for quadratic expressions. It is not even correct on all of these. For example, $Grad[a**x+a**tp[x],x]$ returns $2 tp[a]$. The reason is fundamental mathematics, not programming. If $a$ is a row vector and $x$ is a column vector, then $a**x$ is a number, but $a**tp[x]$ is not.