transition function in Verilog-A

[prcken]

Hi All,
Due to absdelay function can't support AC simulation, so I use transition function instead. I just want to delay the signal from the previous block, not redefining the rise and fall time. But I found after changing to transition function, the results from transient simulation seem not correct. Please advise!
Thanks!

//OptPower(OutOptPower) <+ absdelay((OptPower(InOptPower_top)+OptPower(InOptPower_bot)) * Topt, prop_delay);
//OptPhase(Phase_probe) <+ absdelay(phase_diff,[0]);
OptPower(OutOptPower) <+ transition((OptPower(InOptPower_top)+OptPower(InOptPower_bot)) * Topt, prop_delay);
OptPhase(Phase_probe) <+ transition(phase_diff,[0]);

If neither rise nor fall time are specified, the rise and fall time are taken to be one unit of time (as defined by the timescale complier directive) and no attempt is made to control the time step to follow the trailing corner on the transition.
I am wondering is there any other function can support both tran and ac simulation?