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From |
"Brian P. Poi" <bpoi@stata.com> |

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 coefficients for a quadratic polynomial 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,

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 * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: passing extra information to function evaluator program nl***From:*Ben Zipperer <benzipperer@gmail.com>

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