Solving initial value problem partial differential equation with NDSolve

Question

I'm trying to solve a system of 3 coupled PDEs where I know the values of all three functions at t = 0.

sol = Flatten[NDSolve[{
    \!\(
\*SubscriptBox[\(\[PartialD]\), \(t\)]\(sz[t, z]\)\) == \!\(
\*SubscriptBox[\(\[PartialD]\), \(z, z\)]\(sz[t, z]\)\) + n[t, z] + 
      sy[t, z] - sz[t, z], \!\(
\*SubscriptBox[\(\[PartialD]\), \(t\)]\(sy[t, z]\)\) == \!\(
\*SubscriptBox[\(\[PartialD]\), \(z, z\)]\(sy[t, z]\)\) - 
      sz[t, z], \!\(
\*SubscriptBox[\(\[PartialD]\), \(t\)]\(n[t, z]\)\) == \!\(
\*SubscriptBox[\(\[PartialD]\), \(z, z\)]\(n[t, z]\)\) + sz[t, z] - 
      sy[t, z] , 
    sz[0, z] == DiracDelta[z], sy[0, z] == 0,
     n[0, z] == 0}
   , {sz[t], sy[t], n[t]}, {t, 0, 100}, {z, -100, 100}]]

I get nothing out but this error: NDSolve::ndnum: Encountered non-numerical value for a derivative at t == 0.

I have successfully solved the equations using FTCS in python so I'm not sure what else I need to supply to Mathematica for them to be solved.