Temporary names and Mata matrix operations

[John Mullahy]

Does anyone know why the space after the row-join operator and before the tempname matrix matters in the following?

tempname tn
mata m=J(1,3,2)
mata `tn'=m
mata m \ m
mata m\m
mata `tn' \ `tn'
mata `tn'\(`tn')
mata `tn'\`tn'

. tempname tn

. mata m=J(1,3,2)

. mata `tn'=m

. mata m \ m
       1   2   3
    +-------------+
  1 |  2   2   2  |
  2 |  2   2   2  |
    +-------------+

. mata m\m
       1   2   3
    +-------------+
  1 |  2   2   2  |
  2 |  2   2   2  |
    +-------------+

. mata `tn' \ `tn'
       1   2   3
    +-------------+
  1 |  2   2   2  |
  2 |  2   2   2  |
    +-------------+

. mata `tn'\(`tn')
       1   2   3
    +-------------+
  1 |  2   2   2  |
  2 |  2   2   2  |
    +-------------+

. mata `tn'\`tn'
invalid expression
r(3000);

end of do-file

r(3000);

[Joseph Coveney]

I think that it's a Stata error and not of Mata origin. I can't find it now, but I remember reading somewhere that the reverse solidus is an escape character for the ` character in local macros. See below for illustration.

.ÿlocalÿbÿTextÿhere

.ÿdisplayÿinÿsmclÿasÿtextÿ"`b'"
Textÿhere

.ÿdisplayÿinÿsmclÿasÿtextÿ"\`b'"
`b'

.ÿtempnameÿM

.ÿmatrixÿdefineÿ`M'ÿ=ÿJ(1,ÿ3,ÿ2)

.ÿmatrixÿdefineÿ`M'ÿ=ÿ`M'ÿ\ÿ`M'

.ÿmatrixÿlistÿ`M'

__000001[2,3]
ÿÿÿÿc1ÿÿc2ÿÿc3
r1ÿÿÿ2ÿÿÿ2ÿÿÿ2
r1ÿÿÿ2ÿÿÿ2ÿÿÿ2

.ÿmatrixÿdefineÿ`M'ÿ=ÿJ(1,ÿ3,ÿ2)

.ÿmatrixÿdefineÿ`M'ÿ=ÿ`M'\`M'
__000001`Mÿnotÿfound
r(111);

.

[daniel klein]

I can't find it now, but I remember reading somewhere that the reverse solidus is an escape character for the ` character in local macros.

The issue is discussed in Cox (2008).


Cox, N. J. 2008. Stata tip 65: Beware the backstabbing backslash, The Stata Journal, 8(3), pp. 446--447.

[John Mullahy]

Thanks Joseph and Daniel.