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# st: Simulating time series with if else condition

 From mweberru@students.mail.uni-mannheim.de To statalist@hsphsun2.harvard.edu Subject st: Simulating time series with if else condition Date Tue, 21 Feb 2012 22:53:36 +0100

```Dear Statalist,

```
I would like to generate a time series of debt ratios using Monte Carlo Simulation for ~ 200 firms over 19 years. I start with the debt-level (in \$) in 1971 and add debt-issues/-repayments (in \$, determined via OLS regression with a funds flow deficit as independent variable) to generate next year's debt-level. This process is repeated until 1989, thus generating a series of debt-ratios for each firm from 1971 to 1989.
```
```
The firm is assumed to issue debt if the funds-flow deficit is positive and to repay debt if the deficit is negative. However, debt is only repayed until the debt-level has reached 0.
```
```
I have written a program for this, using the "postfile-"command". However, I am having troubles with adding the condition that the minimum debt level cannot be less than zero. Thus, the problematic part of the following program is the if-else condition.
```
I would be really thankful if anyone of you could help me solve my problem.

Regards,
M.Weber

Here is the do-file:

set seed  75225379

scalar const=0
scalar coeff=0.7

gen u=.
gen x=.
gen debtissue_sim=.
by id: gen debtlevel_sim=.
gen debtratio_sim=.

```
postfile sim debtissue_sim debtlevel_sim debtratio_sim using sim_results, replace
```quietly {
forvalues i=1/1000 {
tsset id fyear
replace u=rnormal()
```
replace x=def /*def: funds flow deficit*/ replace debtissue_sim=const + coeff * x + u /*estimating the level of debt-issue/-repayments*/
```regress debtissue_sim  x
if fyear==1971{
```
```    }
```
else if fyear>1971 & (L.debtlevel_sim+debtissue_sim)<=0 { /*in years following 1971: no negative debt-level*/
```    by id: replace debtlevel_sim=0
}
else {
```
by id: replace debtlevel_sim=L.debtlevel_sim+debtissue_sim /*transform debt-level to debt-ratio*/
```    }
replace debtratio_sim=debtlevel_sim/net_assets
post sim (debtissue_sim) (debtissue_sim_at) (debtlevel_sim) (debtratio_sim)
}
}
postclose sim

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```