[ADMB Users] Adjusted pow function for ADMB-RE

[Stirrup, Oliver]

Hello all

I have found that use of the 'pow' function causes executables created by ADMB to crash when the first argument is zero, i.e. when a calculation of 0^x is attempted.

In my template files, data relating to a time variable are read into a dvar_vector and (within a loop) each element of this vector is then raised to the power of a model parameter. The time variable is positive in most cases, but occasionally takes the value of zero, leading to the problem described.

Using the standard mode for ADMB, I have overcome this problem by defining the following function to replace 'pow':

<<< >>>

GLOBALS_SECTION

  #include <admodel.h>

  dvariable pow2(const dvariable & time, const dvariable & T)
  {
  if(time==0)
    return 0;
  else return pow(time,T);
  }

<<< >>>

I would now like to implement a similar solution for the random effects mode of ADMB, but have so far been unsuccessful in my attempts, with a large number of error messages on compilation. I think that my problem lies in the fact that I do not really understand how to define and manipulate df1b2variable objects.

If anyone can offer a solution or any advice regarding this problem, I would be very grateful.

Best wishes

Oliver


Oliver Stirrup
PhD Student

MRC Clinical Trials Unit at UCL
Institute of Clinical Trials & Methodology
London  UK
e-mail:                          oliver.stirrup.13 at ucl.ac.uk

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