R help - Oct 2020 - Solving a simple linear equation using uniroot give error object 'x' not found

Colleagues,
I am trying to learn to use uniroot to solve a simple linear equation. I define
the function, prove the function and a call to the function works. When I try to
use uniroot to solve the equation I get an error message,
Error in yfu n(x,10,20) : object 'x' not found.

I hope someone can tell we how I can fix the problem

  if(!require(rootSolve)){install.packages("rootSolve")}
  library(rootSolve)

  # Define the function
  yfun <- function(x,diffMean,diffSE) ((abs(diffMean)-x)/diffSE)
  # Prove the function and a call to the function work
  yfun(10,100,10)
  # use uniroot to find a solution to the
  # function in the range -100 to 100
  uniroot(yfun(x,10,20),c(-100,100))


My output:
>   # Define the function
>   yfun <- function(x,diffMean,diffSE) ((abs(diffMean)-x)/diffSE)
>   # Prove the function and a call to the funciton works
>   yfun(10,100,10)
[1] 9
>   # use uniroot to find a solution to the
>   # funciton in the range -100 to 100
>   uniroot(yfun(x,10,20),c(-100,100))
Error in yfun(x, 10, 20) : object 'x' not found

Thank you,
John


John David Sorkin M.D., Ph.D.
Professor of Medicine
Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology and Geriatric
Medicine
Baltimore VA Medical Center
10 North Greene Street
GRECC (BT/18/GR)
Baltimore, MD 21201-1524
(Phone) 410-605-7119
(Fax) 410-605-7913 (Please call phone number above prior to faxing)


	[[alternative HTML version deleted]]

On 06/10/2020 11:00 a.m., Sorkin, John wrote:
> Colleagues,
> I am trying to learn to use uniroot to solve a simple linear equation. I
define the function, prove the function and a call to the function works. When I
try to use uniroot to solve the equation I get an error message,
> Error in yfu n(x,10,20) : object 'x' not found.
> 
> I hope someone can tell we how I can fix the problem
> 
>    if(!require(rootSolve)){install.packages("rootSolve")}
>    library(rootSolve)
> 
>    # Define the function
>    yfun <- function(x,diffMean,diffSE) ((abs(diffMean)-x)/diffSE)
>    # Prove the function and a call to the function work
>    yfun(10,100,10)
>    # use uniroot to find a solution to the
>    # function in the range -100 to 100
>    uniroot(yfun(x,10,20),c(-100,100))
> 
> 
> My output:
>>    # Define the function
>>    yfun <- function(x,diffMean,diffSE) ((abs(diffMean)-x)/diffSE)
>>    # Prove the function and a call to the funciton works
>>    yfun(10,100,10)
> [1] 9
>>    # use uniroot to find a solution to the
>>    # funciton in the range -100 to 100
>>    uniroot(yfun(x,10,20),c(-100,100))
> Error in yfun(x, 10, 20) : object 'x' not found
The problem is that uniroot() wants a function as first argument, and 
yfun(x,10,20) is not a function, it's the value of a function.  You can 
do it with

  uniroot(function(x) yfun(x,10,20),c(-100,100))

which creates the anonymous function

   function(x) yfun(x,10,20)

and passes that to uniroot().

Duncan Murdoch
> 
> Thank you,
> John
> 
> 
> John David Sorkin M.D., Ph.D.
> Professor of Medicine
> Chief, Biostatistics and Informatics
> University of Maryland School of Medicine Division of Gerontology and
Geriatric Medicine
> Baltimore VA Medical Center
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> (Phone) 410-605-7119
> (Fax) 410-605-7913 (Please call phone number above prior to faxing)
> 
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

Have you looked at the examples in ?uniroot? Don't call yfun... let uniroot
do that.

On October 6, 2020 8:00:59 AM PDT, "Sorkin, John" <jsorkin at
som.umaryland.edu> wrote:
>Colleagues,
>I am trying to learn to use uniroot to solve a simple linear equation.
>I define the function, prove the function and a call to the function
>works. When I try to use uniroot to solve the equation I get an error
>message,
>Error in yfu n(x,10,20) : object 'x' not found.
>
>I hope someone can tell we how I can fix the problem
>
>  if(!require(rootSolve)){install.packages("rootSolve")}
>  library(rootSolve)
>
>  # Define the function
>  yfun <- function(x,diffMean,diffSE) ((abs(diffMean)-x)/diffSE)
>  # Prove the function and a call to the function work
>  yfun(10,100,10)
>  # use uniroot to find a solution to the
>  # function in the range -100 to 100
>  uniroot(yfun(x,10,20),c(-100,100))
>
>
>My output:
>>   # Define the function
>>   yfun <- function(x,diffMean,diffSE) ((abs(diffMean)-x)/diffSE)
>>   # Prove the function and a call to the funciton works
>>   yfun(10,100,10)
>[1] 9
>>   # use uniroot to find a solution to the
>>   # funciton in the range -100 to 100
>>   uniroot(yfun(x,10,20),c(-100,100))
>Error in yfun(x, 10, 20) : object 'x' not found
>
>Thank you,
>John
>
>
>John David Sorkin M.D., Ph.D.
>Professor of Medicine
>Chief, Biostatistics and Informatics
>University of Maryland School of Medicine Division of Gerontology and
>Geriatric Medicine
>Baltimore VA Medical Center
>10 North Greene Street
>GRECC (BT/18/GR)
>Baltimore, MD 21201-1524
>(Phone) 410-605-7119
>(Fax) 410-605-7913 (Please call phone number above prior to faxing)
>
>
>	[[alternative HTML version deleted]]
>
>______________________________________________
>R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.
-- 
Sent from my phone. Please excuse my brevity.

... or

uniroot( yfun, c( -100, 100 ), diffMean=10, diffSE=20 )

On October 6, 2020 8:06:35 AM PDT, Duncan Murdoch <murdoch.duncan at
gmail.com> wrote:
>On 06/10/2020 11:00 a.m., Sorkin, John wrote:
>> Colleagues,
>> I am trying to learn to use uniroot to solve a simple linear
>equation. I define the function, prove the function and a call to the
>function works. When I try to use uniroot to solve the equation I get
>an error message,
>> Error in yfu n(x,10,20) : object 'x' not found.
>> 
>> I hope someone can tell we how I can fix the problem
>> 
>>    if(!require(rootSolve)){install.packages("rootSolve")}
>>    library(rootSolve)
>> 
>>    # Define the function
>>    yfun <- function(x,diffMean,diffSE) ((abs(diffMean)-x)/diffSE)
>>    # Prove the function and a call to the function work
>>    yfun(10,100,10)
>>    # use uniroot to find a solution to the
>>    # function in the range -100 to 100
>>    uniroot(yfun(x,10,20),c(-100,100))
>> 
>> 
>> My output:
>>>    # Define the function
>>>    yfun <- function(x,diffMean,diffSE)
((abs(diffMean)-x)/diffSE)
>>>    # Prove the function and a call to the funciton works
>>>    yfun(10,100,10)
>> [1] 9
>>>    # use uniroot to find a solution to the
>>>    # funciton in the range -100 to 100
>>>    uniroot(yfun(x,10,20),c(-100,100))
>> Error in yfun(x, 10, 20) : object 'x' not found
>
>The problem is that uniroot() wants a function as first argument, and 
>yfun(x,10,20) is not a function, it's the value of a function.  You can
>
>do it with
>
>  uniroot(function(x) yfun(x,10,20),c(-100,100))
>
>which creates the anonymous function
>
>   function(x) yfun(x,10,20)
>
>and passes that to uniroot().
>
>Duncan Murdoch
>> 
>> Thank you,
>> John
>> 
>> 
>> John David Sorkin M.D., Ph.D.
>> Professor of Medicine
>> Chief, Biostatistics and Informatics
>> University of Maryland School of Medicine Division of Gerontology and
>Geriatric Medicine
>> Baltimore VA Medical Center
>> 10 North Greene Street
>> GRECC (BT/18/GR)
>> Baltimore, MD 21201-1524
>> (Phone) 410-605-7119
>> (Fax) 410-605-7913 (Please call phone number above prior to faxing)
>> 
>> 
>> 	[[alternative HTML version deleted]]
>> 
>> ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
>______________________________________________
>R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.
-- 
Sent from my phone. Please excuse my brevity.

On Tue, 6 Oct 2020 15:00:59 +0000
"Sorkin, John" <jsorkin at som.umaryland.edu> wrote:
> Colleagues,
> I am trying to learn to use uniroot to solve a simple linear
> equation. I define the function, prove the function and a call to the
> function works. When I try to use uniroot to solve the equation I get
> an error message, Error in yfu n(x,10,20) : object 'x' not found.
> 
> I hope someone can tell we how I can fix the problem
> 
>   if(!require(rootSolve)){install.packages("rootSolve")}
>   library(rootSolve)
Others have told you how to solve your problem.  I am curious to know
why on earth you are loading the rootSolve package.  The uniroot()
function is in package "stats" which is automatically available.

<SNIP>

cheers,

Rolf Turner

-- 
Honorary Research Fellow
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276