c     user amplitude subroutine
      Subroutine vuamp(
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)
      
      include 'vaba_param.inc'

C     svars - additional state variables, similar to (V)UEL
      dimension sensorValues(nSensor), svars(nSvars)
      dimension 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,
     *           iStopAnalysis     = 4,
     *           nFlagsDefine      = 4)
      dimension time(nTime), lFlagsInfo(nFlagsInfo),
     *          lFlagsDefine(nFlagsDefine)
      dimension jSensorLookUpTable(*)

      parameter(timeStarSecStep = 1.0)

C     User code to compute  ampValue = F(sensors)

c     get sensor values first; note that 
      iR_U1  = ivGetSensorID('RIGHTNODESENSOR_U1', jSensorLookUpTable)
      valueR_U1  = sensorValues(iR_U1)      

      if (ampName(1:8) .eq. 'LOADAMP2' ) then
c         lFlagsDefine(iComputeDeriv)    = 1
c         lFlagsDefine(iComputeSecDeriv) = 1
c         lFlagsDefine(iComputeInteg)    = 1

         if (time(iTotalTime).lt.timeStarSecStep) then

c           these sensors are defined only in the first step
c           print them out
            iR_CU1     = ivGetSensorID('ELEM1_SENSOR_CU1',
     *                                  jSensorLookUpTable)
            valueR_CU1 = vGetSensorValue('ELEM1_SENSOR_CU1',
     *                                   jSensorLookUpTable,
     *                                   sensorValues)               
c            call xplb_abqerr(1, 'Sensor %S value: %R',0,valueR_CU1,
c     *                        sensorNames(iR_CU1))

            iR_CRF2     = ivGetSensorID('ELEM1_SENSOR_CRF2',
     *                                  jSensorLookUpTable)
            valueR_CRF2 = vGetSensorValue('ELEM1_SENSOR_CRF2',
     *                                    jSensorLookUpTable,
     *                                    sensorValues)
c            call xplb_abqerr(1, 'Sensor %S value: %R',0,valueR_CRF2,
c     *                        sensorNames(iR_CRF2))

         end if

         if (lFlagsInfo(iInitialization).eq.1) then 
            ampValueNew      = ampValueOld
c            ampDerivative    = 0.0
c            ampSecDerivative = 0.0
c            ampIncIntegral   = 0.0
            if (time(iTotalTime).ge.timeStarSecStep) then
c              store the initial value of the sensor in the initialization
c              phase of the second step
               svars(1) =  valueR_U1
            end if

         else 
c           Example: f(t) = t
            tim = time(iStepTime)
            tStart = tim - dt
            tEnd   = tim 
            
            if (time(iTotalTime).lt.timeStarSecStep) then
               ampValueNew = valueR_U1
            else
               ampValueNew = valueR_U1 - svars(1)
            end if

c            ampDerivative    = 1.0
c            ampSecDerivative = 0.0
c            ampIncInteg      = (tStart*tStart-tEnd*tEnd)/2.0

C           stop the analysis, if desired
            if (ampValueNew.gt.1000) lFlagsDefine(iStopAnalysis)=1
         end if

c      else if (ampName(1:7) .eq. 'LOADAMP' ) then
c         if (lFlagsInfo(iInitialization).eq.1) then 
c            ampDerivative    = 0.0
c            ampSecDerivative = 0.0
c            ampIncIntegral   = 0.0
c            ampValueNew      = ampValueOld
c         else
c           Example: f(t) = t
c            tim = time(iStepTime)
c            tStart = tim - dt
c            tEnd   = tim 
c            ampValueNew      = tim
c            ampDerivative    = 1.0
c            ampSecDerivative = 0.0
c            ampIncInteg      = (tStart*tStart-tEnd*tEnd)/2.0
c         end if

      end if 

      return
      end