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# Re: st: passing extra information to function evaluator program nl

 From "Brian P. Poi" To statalist@hsphsun2.harvard.edu Subject Re: st: passing extra information to function evaluator program nl Date Tue, 23 Mar 2010 12:13:01 -0500 (CDT)

```
On Tue, 23 Mar 2010, Ben Zipperer wrote:

```
```I am interested in using Stata to find a real roots to a single
polynomial several times, where the coefficients vary each time.  I
basically want to apply Newton's method or something else to vectors
of coefficients. I originally planned to restrict the solver at
http://www.stata.com/support/faqs/lang/nl.html to a single polynomial
and then iterate it, changing the coefficients at each iteration.
However, I can't figure out how to pass the coefficients to the
function evaluator program. How do I do this? Do I modify the syntax
statement of the program? Or should I try a different strategy?

For example, let's say the rows of the following matrix form the

mat def M = (1,2,3\ 4,5,6\ 7,8,9)

Then the nl program evaluator program is something like

capture program drop nlpolysolve
program nlpolysolve

syntax varlist(min=1 max=1) [if], at(name)

tempname x z
scalar `x' = `at'[1, 1]
scalar `z' = `at'[1, 2]

tempvar yh
// the real polynomial
gen double `yh' = a_`i' * x^2 + b_`i' * `x' + c_`i' + 1 in 1

replace `yh' = 1 - `z' in 2
replace `varlist' = `yh'

end

And my iterations are something like

forvalues i=1/3 {
preserve
clear
set obs 2
gen y = 0
replace y = 1 in 1

local a_`i' = M[`i',1]
local b_`i' = M[`i',2]
local c_`i' = M[`i',3]

nl polysolve @ y, parameters(A B) initial(A 0.5 B 1)
stuffiwanttopass(a_`i' b_`i' c_i')

restore
}

How do I pass the entries of the matrix to the nlpolysolve program above?

```
```

Ben,

```
Just make your program accept an additional option; any options that -nl- doesn't recognize as belonging to it will get passed to your program. Try something like this:
```

capture program drop nlpolysolve
program nlpolysolve

syntax varlist(min=1 max=1) [if], at(name) mycoefs(numlist)

local a : word 1 of `mycoefs'
local b : word 2 of `mycoefs'
local c : word 3 of `mycoefs'
...

gen double `yh' = `a' * x^2 + `b' * `x' + `c' + 1 in 1

end

...

local a_`i' = M[`i',1]
local b_`i' = M[`i',2]
local c_`i' = M[`i',3]

nl polysolve @ y, parameters(A B) initial(A 0.5 B 1) ///
mycoefs(`a_`i'' `b_`i'' `c_`i'')

-- Brian Poi
-- bpoi@stata.com
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```