This is the old precision issue again in
another guise. Search for precision in
the FAQs and the manuals.
Once more from the top:
You think decimal.
Stata thinks binary.
Sometimes, they just can't match exactly.
(We need a rhyming version of this, and
a catchy tune, so we can all sing it at
users' meetings. On the other hand, perhaps
not.)
I tried this:
. forval i = 1(.1)2 {
2. di %21.18f `i'
3. }
1.000000000000000000
1.100000000000000100
1.200000000000000000
1.300000000000000000
1.399999999999999900
1.500000000000000000
1.600000000000001000
1.700000000000001100
1.800000000000000900
1.900000000000001000
. forval i = 1(.1)2 {
2. di %21x `i'
3. }
+1.0000000000000X+000
+1.199999999999aX+000
+1.3333333333333X+000
+1.4cccccccccccdX+000
+1.6666666666666X+000
+1.8000000000000X+000
+1.999999999999eX+000
+1.b333333333338X+000
+1.cccccccccccd1X+000
+1.e66666666666bX+000
Onnly when your macro is 1.0 and 1.5
can Stata hold the value you want exactly.
This is a consequence of the fact that
10 is not a power of 2.
In general, you will be better off cycling
over integers, and then stepping towards
what you want _inside_ the loop.
Nick
[email protected]
Richard Sherman
> Using Stata 8.2, I am having trouble repeating a process the correct
> number of times using -forvalues-. The range is specified as (e.g.)
>
> forval i = 1(.1)2
>
> Here, 2 is the upper limit of the range. But the final operation
> involving `i' ends at 1.9 rather than 2.
>
> A simple example follows. The second -forval- encloses a command to
> put the value of the counter `i' in a variable repeatedly.
> The first
> -forval- causes this to repeat for different upper limits of the
> inner -forval- loop. The output is a summary of the resulting
> variables. Note the maximum values. I expect the maximum value to
> be 1, then 2, then 3, etc.
>
> . forval u = 1/10 {
> 2. clear
> 3. set obs 100
> 4. gen x = .
> 5. forval i = 1(.1)`u' {
> 6. local n = float(10*(`i'))
> 7. qui replace x = `i' in `n'
> 8. }
> 9. su
> 10. }
> obs was 0, now 100
> (100 missing values generated)
>
> Variable | Obs Mean Std. Dev. Min
> Max
> -------------+--------------------------------------------------------
> x | 1 1 . 1
> 1
> obs was 0, now 100
> (100 missing values generated)
>
> Variable | Obs Mean Std. Dev. Min
> Max
> -------------+--------------------------------------------------------
> x | 10 1.45 .302765 1
> 1.9
> obs was 0, now 100
> (100 missing values generated)
>
> Variable | Obs Mean Std. Dev. Min
> Max
> -------------+--------------------------------------------------------
> x | 20 1.95 .591608 1
> 2.9
> obs was 0, now 100
> (100 missing values generated)
>
> Variable | Obs Mean Std. Dev. Min
> Max
> -------------+--------------------------------------------------------
> x | 30 2.45 .8803408 1
> 3.9
> obs was 0, now 100
> (100 missing values generated)
>
> Variable | Obs Mean Std. Dev. Min
> Max
> -------------+--------------------------------------------------------
> x | 41 3 1.197915 1
> 5
> obs was 0, now 100
> (100 missing values generated)
>
> Variable | Obs Mean Std. Dev. Min
> Max
> -------------+--------------------------------------------------------
> x | 51 3.5 1.486607 1
> 6
> obs was 0, now 100
> (100 missing values generated)
>
> Variable | Obs Mean Std. Dev. Min
> Max
> -------------+--------------------------------------------------------
> x | 61 4 1.775293 1
> 7
> obs was 0, now 100
> (100 missing values generated)
>
> Variable | Obs Mean Std. Dev. Min
> Max
> -------------+--------------------------------------------------------
> x | 71 4.5 2.063977 1
> 8
> obs was 0, now 100
> (100 missing values generated)
>
> Variable | Obs Mean Std. Dev. Min
> Max
> -------------+--------------------------------------------------------
> x | 81 5 2.352658 1
> 9
> obs was 0, now 100
> (100 missing values generated)
>
> Variable | Obs Mean Std. Dev. Min
> Max
> -------------+--------------------------------------------------------
> x | 91 5.5 2.641338 1
> 10
>
> .
> end of do-file
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