[R] Solving a simple linear equation using uniroot give error object 'x' not found

[Jeff Newmiller]

... or

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

On October 6, 2020 8:06:35 AM PDT, Duncan Murdoch <murdoch.duncan using 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]]
>> 
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>>
>
>______________________________________________
>R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
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>and provide commented, minimal, self-contained, reproducible code.

-- 
Sent from my phone. Please excuse my brevity.