Introduction

The renewalCount() function from the countr package is used for counting renewal processes, which are widely used in reliability engineering and other fields of statistics. In this article, we will delve into how to use the renewalCount() function, specifically to fit a Weibull distribution model.

Background

The renewalCount() function relies on an optimization algorithm under the hood, which is responsible for finding the parameters that best fit a given model. The optimization process involves minimizing a loss function and may require the use of various techniques such as gradient descent or quasi-Newton methods. In this case, we are using the optimx package to perform the optimization.

The Problem

The user’s code attempts to call the renewalCount() function with several parameters:

wei <- renewalCount(formula = packets ~ 1,
                     data = dfdata,
                     dist = "weibull",
                     weiMethod = "series_acc",
                     computeHessian = FALSE,
                     control = renewal.control(trace = 0))

The error message returned by R is:

error: Mat::init(): requested size is too large; suggest to enable ARMA_64BIT_WORD
Error in optimx.check(par, optcfg$ufn, optcfg$ugr, optcfg$uhess, lower,  : 
  Cannot evaluate function at initial parameters

This error occurs when the optimization algorithm fails to find a suitable set of parameters for the model. In this case, it seems that the requested size is too large.

The ARMA_64BIT_WORD Issue

The ARMA_64BIT_WORD option controls whether R should use 64-bit words in its arithmetic operations. When working with optimization algorithms that require floating-point calculations, using 64-bit words can help mitigate issues related to integer overflows or precision losses.

Enabling ARMA_64BIT_WORD in RStudio

To enable ARMA_64BIT_WORD in RStudio, you need to run the following command:

> options("ARMA_64BIT_WORD")

This will set the ARMA_64BIT_WORD option to 1. You can also set this option when running your R code using the --options flag:

R --options ARMA_64BIT_WORD=1

Alternative Solutions

As an alternative, you could try importing the optimx and RcppArmadillo libraries as suggested in the original question. However, this may not necessarily solve the problem at hand.

Another approach is to use a different optimization algorithm that does not rely on floating-point calculations or 64-bit words. The countr package provides several options for customization of the optimization process, which may help resolve the issue.

Modifying the Control Options

To customize the control options for the renewalCount() function, you can use the control argument:

wei <- renewalCount(formula = packets ~ 1,
                     data = dfdata,
                     dist = "weibull",
                     weiMethod = "series_acc",
                     computeHessian = FALSE,
                     control = renewal.control(trace = 0))

You can modify the control argument to change various aspects of the optimization process. For example, you could try increasing the maximum number of iterations or decreasing the tolerance for convergence:

wei <- renewalCount(formula = packets ~ 1,
                     data = dfdata,
                     dist = "weibull",
                     weiMethod = "series_acc",
                     computeHessian = FALSE,
                     control = renewal.control(trace = 0, maxiter = 100, tol = 1e-6))

Conclusion

In conclusion, the renewalCount() function from the countr package can be used to fit a Weibull distribution model. However, it may require additional tweaking of control options or using alternative optimization algorithms to resolve issues related to integer overflows or precision losses.

We have discussed how to enable ARMA_64BIT_WORD in RStudio and customized the optimization process using the control argument. Additionally, we mentioned some alternative solutions that may help resolve the issue at hand.

Last modified on 2024-02-24