derv:=proc(neqn,t,u,ut)
#
# Function derv computes the derivative vector 
# of the linear PDE problem
#
# Type variables
  local xl, xu, dx, dxs, i:
#
# Problem parameters
  xl:=0.0:
  xu:=1.0:
#
# BC at x = 0
   u[1]:=0.0:
  ut[1]:=0.0:
#
# BC at x = 1
   u[neqn]:=0.0:
  ut[neqn]:=0.0:
#
# Interior points
  dx:=(xu-xl)/(neqn-1):
  dxs:=dx*dx:
  for i from 2 to neqn-1 do
     ut[i]:=(u[i+1]-2.0*u[i]+u[i-1])/dxs:
  end do:
#
# End of derv
  end: