# [R] Help with a simple subroutine

Ebert,Timothy Aaron tebert @end|ng |rom u||@edu
Fri Sep 9 14:39:48 CEST 2022

```If t = 1/sqrt(v[2,2]) and there is no code to change the value of v[2,2] and no code to change to a different cell why would you get two different values?

One approach to debugging is to make a small example and see if the code output matches (line-by-line) the output you get from doing a manual calculation. If they do not match you at least know where to start looking for a problem. Hand calculation can use pencil and paper or Excel or other tools. It is a tedious task but very effective.

Tim

-----Original Message-----
From: R-help <r-help-bounces using r-project.org> On Behalf Of Ivan Krylov
Sent: Friday, September 9, 2022 5:03 AM
To: Steven T. Yen <styen using ntu.edu.tw>
Cc: R-help Mailing List <r-help using r-project.org>
Subject: Re: [R] Help with a simple subroutine

[External Email]

В Fri, 9 Sep 2022 16:46:00 +0800
"Steven T. Yen" <styen using ntu.edu.tw> пишет:

> I am expecting the line  t<-gamma/sgamma to produce two different
> values. But I confirm that it is doing tt<-gamma[1]/sgamma[1]

No, it just happens that gamma[1]/sgamma[1] is the same as gamma[2]/sgamma[2], subject to rounding errors:

> +   gamma<-exp(b)
> +   vgamma<-gamma^2*v[2,2]
> +   sgamma<-sqrt(vgamma)
> +   t<-gamma/sgamma

t = gamma / sgamma = gamma / sqrt(gamma^2 * v[2,2]) =
= gamma / (abs(gamma) * sqrt(v[2,2])) = (given gamma = exp(b) > 0)
= 1 / sqrt(v[2,2]).

--
Best regards,
Ivan

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