Delete a matrix trace

[Marc Audrna]

Hello,

I would like to know how to delete the trace of a matrix. I do not find it in the "help".
Thank you

[Jesse Wursten]

What do you mean with delete?

[Marc Audrna]

I dont know the exact term

I have :

	A	B	C
a	4	5	3
b	5	12	7
c	25	48	9

I want

	A	B	C
a		5	3
b	5		7
c	25	48

[Charlie Joyez]

Marc,
Do you want the diagonal to be missing values (.) or zeros? You can't have blanks (strings "") in a mata matrix altogether with reals.

If you want them to be zeros, it is easy enough :

M= (4,5,3 \ 5,12,7 \25,48,9)
N=M-diag(M)

Charlie

[Marc Audrna]

I shall prefer missing values.
I think I have a problem of translation between French and English. A trace in French is a diagonal matrix in English.

[Rafal Raciborski (StataCorp)]

mata:
X = runiform(5,5)
X
_diag(X,.)
X
end

[Charlie Joyez]

I shall prefer missing values.
I think I have a problem of translation between French and English. A trace in French is a diagonal matrix in English.

Well not exactly, even in French, the trace of a matrix (the equivalent term also exists in English) is the sum of the diagonal elements, so is only a scalar, when the diagonal is actually a vector containing the diagonal elements.

Concerning your initial question, Rafal gave you the code you need.

Best,
Charlie

[Marc Audrna]

Thank you for you answers.
But, none of the two method runs.

when I type :

mat N=X-diag(X)

Stata returns "conformability error". Yet, I run a square matrix X(37,37).

And when I type

_diag(X,.)

Stata returns "unrecognized command: _diag".

I think that I miss a stage...?

Precisions :
I import an Excel sheet and I make a matrix whith mkmat function

[Charlie Joyez]

Marc,
Do you write on Stata or on Mata?
as Rafal precised, you have to type both codes under these two delimiters:

mata:

end

And your Matrices should be mata matrices and not Stata ones (we are on the Mata forum).


Actually, I find the same error message as you when I run under Stata, so I think this is the problem.

*Under Stata
matrix define X=(2,2 \ 3,3)
matrix list
mat N=X-diag(X)
*returns conformability error

_diag(X,.)
*returns unrecognized command:  _diag

To define you matrix on mata:

mata :
X=(2,2 \ 3,3)
X
mat N=X-diag(X)
*does not returns error code
N

_diag(X,.)
X
end

Best,
Charlie

[Marc Audrna]

Okay !
I do not use stata every day and I have some gaps...
Is it possible to make what I whant with stata or must I make it with mata ?
I have difficulty understanding how to pass from stata to mata...
Can I use mata with Do-file Editor ?

[Christophe Kolodziejczyk]

use st_matrix to pass matrices to mata back and forth.
for example

mat sX = matuniform(5,5)
mat li sX

mata:
mX = st_matrix("sX")
_diag(mX,.)
st_matrix("sX",mX)

end

mat li sX

[Marc Audrna]

Thank you very much to all of you !