Boundary conditions for PDE

Hello, I'm trying to solve the PDE equation for function v(t,s), the boundary conditions are lim(v(t,s))=0 s->Infitity DvDs(t,0)=0

I wrote the function for these conditions to call it in pdepe, but it doesn't work Matlab writes that variable DvDs(DvlDsv) is undefined and "Undefined function 'limit' for input arguments of type 'double'."

function [ pl,ql,pr,qr ] = bc1( sl,vl,sr,vr,t )
%bc1 Bounrary conditions
pr=DvDs; % or DvrDsr
qr=0;
pl=limit(vr,sr=infinity);
ql=0;
end

I will be glad if you give me some advice for this problem, thanks.