# st: Re: Putting variable ylines in a graph

 From "Nick Cox" <[email protected]> To <[email protected]> Subject st: Re: Putting variable ylines in a graph Date Thu, 21 Jan 2010 19:54:16 -0000

```-yline()- is strict: it needs a numlist. However, you can do calculations on the fly using a standard construct.

rvfplot, yli(`=-2*e(rmse)' `=2*e(rmse)')

The `=exp' syntax is explained at -help macro-.

If you type `=2 * e(rmse)', for example, Stata reads this as

1. Do the calculation 2 * e(rmse)

2. Insert the result at this place so that the command being typed can see it.

Thus -yline()- is pretty dumb and certainly contains no hidden calculator, but the rest of Stata is up to doing what you want.

As usual, start with a left quote ` and finish with a right quote '.

Nick
[email protected]

From: Lachenbruch, Peter [mailto:[email protected]]

I am using rvfplot to graph residuals and I would like to draw lines at -2 sd and 2 sd limits.
My thought was to use rvfplot, yline(-2*e(rmse) 2*e(rmse))
But Stata did not like it:

. rvfplot,yline(2*e(rmse) 2*e(rmse))
invalid line argument, -2*(e(rmse) 2*e(rmse)
r(198);

I tried setting the limits to a scalar or a local scalar, but I got the same result (I had set scalar L= 2*e(rmse) )
.rvfplot,yline(-L L)
invalid line argument, -L L
r(198)

Is there a way to do this or does yline require numbers rather than functions?
I could do several twoway plots (one for residuals,one for the upper limit, one for the lower limit), but this seems a bit cumbersome

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