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From |
Ben Jann <ben.jann@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Mata st_store problem with selectvar (using mm_root) |

Date |
Wed, 11 Feb 2009 21:38:17 +0100 |

Think of what you are asking Mata to do. st_store(1, ...) means: "Write something to observation 1." If you type st_store(1, "x", "rc", x) (or -st_store(1, "x", 1, x)- if rc is the first variable) and variable "rc" is zero for the first observation, this means: "Write x to no observation". "no observation" has zero rows, but x is a scalar in your example and therefore has 1 row. Hence the conformability error. You could code, e.g. rc = (mm_root(x = .,&myfunc(),0,1,0,1000,a)==0) if (rc) st_store(1, "x", x) ben On Wed, Feb 11, 2009 at 4:25 PM, Bob Hammond <robert_hammond@ncsu.edu> wrote: > All, > > I want to store a Mata scalar in my Stata data set using st_store(), but > only in certain cases, as determined by selectvar. My reading of the > st_data() help file (where st_store() directs you to concerning selectvar) > says that the following should work: > > clear > cap mata: mata drop myfunc() > set obs 1 > gen double rc = . > gen double x = . > mata > function myfunc(x, a) return(x^2 - a) > a = 2 > rc = (mm_root(x = .,&myfunc(),0,1,0,1000,a)==0) > st_store(1,"rc",rc) > st_store(1,"x",1,x) > end > list > > My Stata variable "rc" is equal to one if the mm_root() function has found a > valid solution. I only want st_store() to write the solution to the data > set when it is valid. > > Instead, the program correctly writes the solution to the data set when it > is valid (try by changing a to "a = 2/3" above) but generates a "3200 > conformability error" when it is invalid (try the program as written above, > which generates no valid solution because it looks between 0 and 1 for the > square root of 2). > Maybe this is a simple error in my reading of how to use selectvar but I > have tried it by placing "rc" and, alternatively, by placing 1 (the variable > number of "rc") in the third argument of st_store(). Both ways give the > same conformability error. > > Any thoughts would be appreciated. Thanks in advance, > > Bob > -- > ------------------------------------------------------------------------ > Bob Hammond > Department of Economics > North Carolina State University > Office: (919) 513-2871 > Fax: (919) 515-7873 > http://www4.ncsu.edu/~rghammon/ > * > * 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/ > * * 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: Mata st_store problem with selectvar (using mm_root)***From:*Bob Hammond <robert_hammond@ncsu.edu>

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