mf_diag.hlp

是一个经济学管理应用软件 很难找的 但是经济学学生又必须用到

{smcl}
{* 16mar2005}{...}
{bf:help mata diag()}
{hline}
{* index diag()}{...}
{* index extract diagonal}{...}
{* index diagonal matrix}{...}

{title:Title}

{p 4 8 2}
{bf:[M-5] diag() -- Create diagonal matrix}


{title:Syntax}

{p 8 12 2}
{it:numeric matrix}
{cmd:diag(}{it:numeric matrix Z}{cmd:)}

{p 8 12 2}
{it:numeric matrix}
{cmd:diag(}{it:numeric vector z}{cmd:)}


{title:Description}

{p 4 4 2}
{cmd:diag()} creates diagonal matrices.

{p 4 4 2}
{cmd:diag(}{it:Z}{cmd:)}, {it:Z} a matrix, extracts the principal diagonal 
of {it:Z} to create a new matrix.  {it:Z} must be square.

{p 4 4 2}
{cmd:diag(}{it:z}{cmd:)}, {it:z} a vector, creates a new matrix with 
the elements of {it:z} on its diagonal.


{title:Remarks}

{p 4 4 2}
Do not confuse {cmd:diag()} with its functional inverse, 
{cmd:diagonal()}; see 
{bf:{help mf_diagonal:[M-5] diagonal()}}.
{cmd:diag()} creates a matrix from a vector (or matrix); 
{cmd:diagonal()} extracts the diagonal of a matrix into a vector.

{p 4 4 2}
Use of {cmd:diag()} should be avoided because it is wasteful of memory.
The colon operators will allow you to use vectors directly:

		Desired calculation         equivalent
		{hline 45}
		{cmd:diag(}{it:v}{cmd:)*}{it:X}, 
		     {it:v} a column              {it:v}{cmd::*}{it:X}
		     {it:v} a row                 {it:v}{bf:'}{cmd::*}{it:X}
		     {it:v} a matrix              {cmd:diagonal(}{it:v}{cmd:):*}{it:X}

	        {it:X}{cmd:*diag(}{it:v}{cmd:)}
		     {it:v} a column              {it:X}{cmd::*}{it:v}{bf:'}
		     {it:v} a row                 {it:X}{cmd::*}{it:v}
		     {it:v} a matrix              {it:X}{cmd::*diagonal(}{it:v}){bf:'}
		{hline 45}

{p 4 4 2}
In the above table, it is assumed that {it:v} is real.  If {it:v} might be
complex, the transpose operators that appear must be changed to
{cmd:transposeonly()} calls, because we do not want the conjugate.  For
instance, {it:v}{bf:'}{cmd::*}{it:X} would become
{cmd:transposeonly(}{it:v}{cmd:):*}{it:X}.


{title:Conformability}

    {cmd:diag(}{it:Z}{cmd:)}:
		{it:Z}:  {it:m x n}
	   {it:result}:  min({it:m},{it:n}) {it:x} min({it:m},{it:n})

    {cmd:diag(}{it:z}{cmd:)}:
		{it:z}:  {it:1 x n}  or  {it:n x 1}
	   {it:result}:  {it:n x n}


{title:Diagnostics}

{p 4 4 2}
None.


{title:Source code}

{p 4 4 2}
{view diag.mata, adopath asis:diag.mata}


{title:Also see}

{p 4 13 2}
Manual:  {hi:[M-5] diag()}

{p 4 13 2}
Online:  help for 
{bf:{help mf_diagonal:[M-5] diagonal()}},
{bf:{help mf_isdiagonal:[M-5] isdiagonal()}};
{bf:{help m4_manipulation:[M-4] manipulation}}
{p_end}