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From |
Bjorn Persson <bpersson@bu.edu> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: recursively defined variables |

Date |
Fri, 16 Sep 2005 14:10:26 -0400 |

Dear Statalist,

I received a very helpful answer (from Nick Cox) to the problem I posted yesterday re recursive variables, as well as a reference to Roger Newson's useful Stata Tip in Stata Journal 4(4) 2004. However, when I try to replicate the examples in Newson's note I keep getting the error message " obs.nos. out of range" after the command:

replace y = y[_n-1] +... (from Newson's Fibonacci sequence example)

Any ideas on what's going wrong here?

(Sorry if this is a double posting - my first mail seems not to have gone through)

Best,

Bjorn

Nick Cox wrote:

This notation I understand to mean

xt -> x at time t xt-1 -> x at time t - 1

x1 -> x at time 1

If so, you initialise

gen x = z in 1

and then you replace

replace x = b * x[_n-1] + z in 2/l

where I guess b is a place-holder for a number you know and note that "l" stands for "l"ast.

The principle is given by the title

of a useful Stata Tip by Roger Newson:

generate and replace use the current sort order. Stata Journal 4(4):484--485 (2004)

Nick n.j.cox@durham.ac.uk

bpersson@bu.edu

I was wondering if anybody could help me to define a variable

recursively in stata? That is, I would like define each observation x

as the sum of a flow variable, z, and the lagged x variable,

discounted by a factor b:

xt = zt + b*xt-1

The three first x variables would then be:

x1 = z1

x2 = z2 + b*z1

x3 = z3 + b*z2 + b^2*z1

and so on).

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**Follow-Ups**:**Re: st: recursively defined variables***From:*Bjorn Persson <bpersson@bu.edu>

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