derv:=proc(neqn,t,u,ut)
#
# Procedure derv computes the derivative vector
# of the 2 x 2 ODE problem
#
# Type variables
  global a, b:
#
# Problem parameters
  a:=5.5:
  b:=4.5:
#
# Derivative vector
  ut[1]:=-a*u[1]+b*u[2]:
  ut[2]:= b*u[1]-a*u[2]:
#
# End of derv
  end: