c     user amplitude subroutine
      Subroutine uamp(
C          passed in for information and state variables
     *     ampName, time, ampValueOld, dt, nProps, props, nSvars, svars,
     *     lFlagsInfo, nSensor, sensorValues, sensorNames, 
     *     jSensorLookUpTable, 
C          to be defined
     *     ampValueNew, 
     *     lFlagsDefine,
     *     AmpDerivative, AmpSecDerivative, AmpIncIntegral,
     *     AmpIncDoubleIntegral)
      
      include 'aba_param.inc'

C     svars - additional state variables, similar to (V)UEL
      dimension sensorValues(nSensor), svars(nSvars), props(nProps)
      character*80 sensorNames(nSensor)
      character*80 ampName

C     time indices
      parameter (iStepTime        = 1,
     *           iTotalTime       = 2,
     *           nTime            = 2)
C     flags passed in for information
      parameter (iInitialization   = 1,
     *           iRegularInc       = 2,
     *           nFlagsInfo        = 2)
C     optional flags to be defined
      parameter (iComputeDeriv       = 1,
     *           iComputeSecDeriv    = 2,
     *           iComputeInteg       = 3,
     *           iComputeDoubleInteg = 4,
     *           iStopAnalysis       = 5,
     *           iConcludeStep       = 6,
     *           nFlagsDefine        = 6)
      dimension time(nTime), lFlagsInfo(nFlagsInfo),
     *          lFlagsDefine(nFlagsDefine)
      dimension jSensorLookUpTable(*)

c     get sensor values first
      vN1_U1   = GetSensorValue('N1_SENSOR_U1',jSensorLookUpTable,
     *                           sensorValues)
      vN251_U1 = GetSensorValue('N251_SENSOR_U1',jSensorLookUpTable,
     *                            sensorValues)
      vN1001_U1 = GetSensorValue('N1001_SENSOR_U1',jSensorLookUpTable,
     *                             sensorValues)
      vN1251_U1 = GetSensorValue('N1251_SENSOR_U1',jSensorLookUpTable,
     *                             sensorValues)
      uAve = 0.25*(vN1_U1 +  vN251_U1 + vN1001_U1 + vN1251_U1)
c
      vN1_RF1   = GetSensorValue('N1_SENSOR_U1',jSensorLookUpTable,
     *                           sensorValues)
      vN251_RF1 = GetSensorValue('N251_SENSOR_U1',jSensorLookUpTable,
     *                            sensorValues)
      vN1001_RF1 = GetSensorValue('N1001_SENSOR_U1',jSensorLookUpTable,
     *                             sensorValues)
      vN1251_RF1 = GetSensorValue('N1251_SENSOR_U1',jSensorLookUpTable,
     *                             sensorValues)
      rfAve = 0.25*(vN1_RF1 + vN251_RF1 + vN1001_RF1 + vN1251_RF1)

      vN100_V1  = GetSensorValue('N100_SENSOR_V1',jSensorLookUpTable,
     *                             sensorValues)
      vN1100_V1 = GetSensorValue('N1100_SENSOR_V1',jSensorLookUpTable,
     *                             sensorValues)
      vAve = 0.5*(vN100_V1  + vN1100_V1)

      vN200_A1  = GetSensorValue('N200_SENSOR_A1',jSensorLookUpTable,
     *                             sensorValues)
      vN1200_A1 = GetSensorValue('N1200_SENSOR_A1',jSensorLookUpTable,
     *                             sensorValues)
      aAve = 0.5*( vN200_A1  + vN1200_A1)

      if (ampName(1:8) .eq. 'LOADAMP2' ) then

C        User code to compute  ampValue = F(sensors)
         if (lFlagsInfo(iInitialization).eq.1) then 
            ampValueNew      = ampValueOld
         else 
c           Example: f(t) = t
            tim = time(iStepTime)
            tStart = tim - dt
            tEnd   = tim 
            
            ampValueNew = uAve  + vAve*dt + 0.5*aAve*dt*dt

C           stop the analysis, if desired
            if (rfAve.gt.1000000) lFlagsDefine(iStopAnalysis)=1
         end if

      end if 

      return
      end