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Re: st: digits difference between stata and mata
From
Wu Zhang <[email protected]>
To
"[email protected]" <[email protected]>
Subject
Re: st: digits difference between stata and mata
Date
Mon, 13 May 2013 19:23:49 -0700 (PDT)
Hi Nick,
Thanks for your contribution to this list.
I have a very strange question: I used "spreg" to run spatial regression; in its manual that command is equivalent to a two-step method which can be implemented in Mata; I did the "spreg" and Mata two weeks ago and the results were the same. But when I repeated the process yesterday, the results were different: the same data set with the same code as before. I am trying to figure out where the difference comes from.
Any thought would be appreciated!
Wu
----- Original Message -----
From: Nick Cox <[email protected]>
To: "[email protected]" <[email protected]>
Cc:
Sent: Monday, May 13, 2013 7:24 PM
Subject: Re: st: digits difference between stata and mata
I don't know what you understand here by "like regression" but formats
assigned by -format- are by definition display formats and have no
effect on what is stored and therefore no effect on the results of
calculation.
Among other arguments, numeric formats controlling the number of
decimal places shown in displays have no bearing on the binary
representation of numbers.
There are many discussions, including
http://www.stata-journal.com/article.html?article=dm0067
Nick
[email protected]
On 13 May 2013 22:11, Wu Zhang <[email protected]> wrote:
>
> Thanks!
>
> By the way, does the format change the calculation results, like regression?
>
> ________________________________
> From: Nick Cox <[email protected]>
>
> Please note: "Stata", "Mata", as at
>
> http://www.stata.com/support/faqs/resources/statalist-faq/#spell
>
> What you see is is likely just to be a side-effect of different
> default formats. You can arrange the same format. Look at -help
> format-.
>
> . sysuse auto
> (1978 Automobile Data)
>
> . gen gpm = 1/mpg
>
> . list gpm in 1/10
>
> +----------+
> | gpm |
> |----------|
> 1. | .0454545 |
> 2. | .0588235 |
> 3. | .0454545 |
> 4. | .05 |
> 5. | .0666667 |
> |----------|
> 6. | .0555556 |
> 7. | .0384615 |
> 8. | .05 |
> 9. | .0625 |
> 10. | .0526316 |
> +----------+
>
> . mata
> ------------------------------------------------- mata (type end to
> exit) ---------------
>
> : gpm2 = st_data(., "gpm")
>
> : gpm2[(1..10)]
> 1
> +---------------+
> 1 | .0454545468 |
> 2 | .0588235296 |
> 3 | .0454545468 |
> 4 | .0500000007 |
> 5 | .0666666701 |
> 6 | .055555556 |
> 7 | .0384615399 |
> 8 | .0500000007 |
> 9 | .0625 |
> 10 | .0526315793 |
> +---------------+
>
> : strofreal(gpm2[(1..10)], "%5.4f")
> 1
> +----------+
> 1 | 0.0455 |
> 2 | 0.0588 |
> 3 | 0.0455 |
> 4 | 0.0500 |
> 5 | 0.0667 |
> 6 | 0.0556 |
> 7 | 0.0385 |
> 8 | 0.0500 |
> 9 | 0.0625 |
> 10 | 0.0526 |
> +----------+
>
> : end
> -----------------------------------------------------------------------------------------
>
> . format gpm %5.4f
>
> . list gpm in 1/10
>
> +--------+
> | gpm |
> |--------|
> 1. | 0.0455 |
> 2. | 0.0588 |
> 3. | 0.0455 |
> 4. | 0.0500 |
> 5. | 0.0667 |
> |--------|
> 6. | 0.0556 |
> 7. | 0.0385 |
> 8. | 0.0500 |
> 9. | 0.0625 |
> 10. | 0.0526 |
> +--------+
>
> Nick
> [email protected]
>
>
> On 13 May 2013 07:50, Wu Zhang <[email protected]> wrote:
>
>> I have a variable list which has different digits after being imported into MATA; I take a snap of the whole picture:
>>
>> In stata:
>>
>> --------------------------------------------
>> 1. 9.477003 8.210668 59.375 -2.00877
>> 2. 9.34036 9.473704 66.0647 -1.543392
>> 3. 8.986102 8.188967 53.92946 -.5894488
>> 4. 9.285332 9.773379 73.92938 -.2278635
>> 5. 9.286468 9.812742 57.82097 -.0813199
>>
>>
>>
>> While in MATA:
>> 1 9.477003098 8.21066761 59.375 -2.008770227
>> 2 9.340359688 9.473704338 66.0647049 -1.54339242
>> 3 8.986102104 8.188966751 53.92946243 -.5894488096
>> 4 9.285331726 9.773379326 73.92938232 -.2278635055
>> 5 9.286467552 9.812742233 57.82096863 -.0813199058
>>
>>
>> Note that what we see in STATA is the same as in the data editor view.
>>
>>
>> I am just wondering whether there is a way to make them the same?
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