PharmPK Discussion - Cumulative Weibull expression

• On 8 Oct 2010 at 13:22:24, (Angusmdmclean.-at-.aol.com) sent the message
  

  
  The cumulative form of the Cumulative Weibull equation with intercepts  is immediately below:
   y=a+b(1-exp(-((x+dln(2)1/e-c)/d)e))
   I have tried to get it to run in WinNonlin as a user model as follows:
  
  remark  equation  y=a+b(1-exp(-((x+dln(2)**1/e-c)/d)**e))
  F is percent dissolved and X is time. b is intercept on y axis, and e is  the intercept on the x axis.
  remark - define model-specific commands COMMANDS NPARAMETERS 5 PNAMES "a", "c", "b", "d", "e"
  END
  FUNC 1
  expon = -((x+dln(2)**1/e-c)/d)**e)
  F =  a+b(1-exp(expon)
   END
  EOM
   With an x, y data set file in place the program did not run.  Please can  I be advised as to the code which will run?
  
  Angus McLean
  
  

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• On 12 Oct 2010 at 03:04:47, Simon Davis (Simon.Davis.at.certara.com) sent the message
  

  
  The following message was posted to: PharmPK
  
  Angus,
         What exactly is the error message you are seeing? It could be an  issue to do with your initial estimates for instance; if you log this  with support.-at-.pharsight.com they can point you to possible options to  resolve the problem.
  
       You may also seek out tips and discuss Pharsight products with  other users at ww.pharsight.com/extranet (free access but a login is  required)
  
       Lastly to assist with users upgrade planning please be aware that  Phoenix WinNonlin 6.2 will be due at the end of the year and will  support the IVIVC tool kit, AutoPilot as well as some minor general  fixes and NLME enhancements.  (That said a 'typical' NCA user should be  fine with 6.1).
  
   Best regards,
                        Simon.
  --
  Simon.Davis.aaa.certara.com
  Senior Scientific Consultant
  Pharsight- A Certara(tm) Company
  
  

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• On 12 Oct 2010 at 15:27:34, (Angusmdmclean.at.aol.com) sent the message
  

  
  Tuesday October 12, 2010:
  
  Simon:  the error message I get is INVALID STATEMENT at the line  beginning
   expon
  It may be a question of how the equation is written in the code.
  
  I repeat as previous see below.
   The cumulative form of the Cumulative Weibull equation with intercepts  is immediately below:
  y=a+b(1-exp(-((x+dln(2)1/e-c)/d)e))
  I have tried to get it to run in WinNonlin as a user model as follows:
  
  remark  equation  y=a+b(1-exp(-((x+dln(2)**1/e-c)/d)**e))
  F is percent dissolved and X is time. b is intercept on y axis, and e is  the intercept on the x axis.
  remark - define model-specific commands COMMANDS NPARAMETERS 5 PNAMES "a", "c", "b", "d", "e"
  END
  FUNC 1
  expon = -((x+dln(2)**1/e-c)/d)**e)
  
  [How about
  
  expon = -((x + (d * ln(2)**(1/e)) - c)/d)**e)
  
  The dln at least should be d*ln - db]
  
  F =  a+b(1-exp(expon)
  
  END
  EOM
  
  With an x, y data set file in place the program did not run.  Please can  I be advised as to the code which will run?
  
  Angus McLean
  
  

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• On 13 Oct 2010 at 20:35:28, Sri Duvvuri (pkscientist.aaa.live.com) sent the message
  

  
  Natural log in Winnonlin is implemented as DLOG( ) or LOGE( ). There  were also some unmatched parantheses in the code. If I  understand your  equation correctly, then its implementation should be something like:
   FUNCTION 1
  expon = -(((x+d*DLOG(2)**1/e-c)/d)**e) F = a+b*(1-exp(expon))
  END
  EOM
   In past, I used the following form of Weibull
  
  c = lag time
  d=shape factor
  e=constant
   FUNCTION 1
  Tdiff=x-c
  if Tdiff>0 then
  expon=-((Tdiff)**d)/e
  else
  expon=0
  endif
  F = a+b*(1-exp(expon))
  END
  EOM
  
  Hope this helps
  
  

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