= Envelope
{disambiguate=mathematics}
{title2=$F(x,y,s)=0,\quad\partial_sF(x,y,s)=0$}
{wiki}
= Geometric envelope
{synonym}
= Envelope
{synonym}
A <geometric envelope> is a <curve> tangent to the members of a smoothly varying family of <curves>. For a regular implicit family $F(x,y,s)=0$, candidate contact points also satisfy the <partial derivative> condition $\partial_sF=0$; regularity is needed to turn these candidates into an actual envelope. The <Mach cone> is a three-dimensional analogue for expanding <spheres>.
Back to article page
