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  GenStat  ~  Use of SUBMAT function to get pieces of a symmetric matrix

AndrewMc
Posted: Wed Aug 01, 2018 10:56 pm Reply with quote
Joined: 28 Jul 2008 Posts: 76
Thankyou David for the explanation of SUBMAT.
I had completely forgotten about the ELEMENTS function, but am now using it to get the values I want, thanks to your clear example code.

Cheers,
Andrew Mc

Andrew McLachlan
Biometrician

-----Original Message-----
From: GENSTAT-Request [mailto:GENSTAT@jiscmail.ac.uk] On Behalf Of David Baird
Sent: Wednesday, 1 August 2018 5:18 p.m.
To: GENSTAT@JISCMAIL.AC.UK
Subject: Re: Use of SUBMAT function to get pieces of a symmetric matrix

Dear Andrew,

SUBMAT assumes that the matrix has a pointer for the rows labels.

VARIATE W,X,Y,Z
SYMMETRIC [ROWS=!P(W,X,Y,Z)] SX; VALUES=!(1...10) PRINT SX; DEC=0 SYMMETRIC [ROWS=!P(W,X)] S1 CALC S1 = SUBMAT(SX) PRINT S1; DEC=0

If you want to access by position use the ELEMENTS function with two arguments (one for rows and one for columns). You need to type the results as symmetric matrices or else the will come out as regular matrices:

SYMMETRIC [4] S; !(1...10)
SYMMETRIC S1,S2
CALC First,Last = !(1...2),!(3...4)
CALC S1,S2 = ELEMENT(2(S);First,Last;First,Last)
PRINT S1,S2; DEC=0

Regards, David.
______________________________________________
Dr David Baird      Statistical Consultant and GenStat Developer VSN (NZ) Limited (David@VSN.CO.NZ)
8 Mariposa Crescent, Aidanfield, Christchurch 8025, New Zealand Ph +64 3 3350588 Cell +64 21 1160803

-----Original Message-----
From: GENSTAT-Request <GENSTAT@jiscmail.ac.uk> On Behalf Of Andrew McLachlan
Sent: 1 August 2018 4:54 PM
To: GENSTAT@JISCMAIL.AC.UK
Subject: Use of SUBMAT function to get pieces of a symmetric matrix

Hi All

I want to get sub-triangles from a symmetric matrix. The Help has lead me to the SUBMAT function, but after reading the Help I still don't understand how to get the function to work. Does anyone have a simple example that they could show me?

For example, with a symmetric matrix with four rows:
1
2, 3
4, 5, 6
7, 8, 9, 10

I wish to get sub-triangles:
1
2, 3

and
6
9, 10


Cheers,
Andrew Mc

Andrew McLachlan
Biometrician



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