{smcl}
{bf:Mata course:  Subscripting}
{hline}

{title:1.  Basic subscripts}

	syntax             meaning 
	{hline 38}
	{it:x}{cmd:[}{it:i}{cmd:,} {it:j}{cmd:]}            ({it:i}, {it:j}) element of {it:x}
	{it:x}{cmd:[}{it:i}{cmd:]}               {it:i}th element of {it:x}
	{hline 38}

{p 4 4 2}
Notes:

{p 8 11 2}
--
{it:x}{cmd:[}{it:i}{cmd:]} is allowed only if 
{it:x} is {it:r x 1} or {it:1 x c}{break}

{p 8 11 2}
--
may be used on left or right side of equal sign

{p 14 17 2}
--
	{cmd:z = x[i,j]}

{p 14 17 2}
--
	{cmd:x[i,j] = z}

{p 8 11 2}
--
very fast



{title:2.  Entire rows and columns}

	syntax             meaning 
	{hline 38}
	{it:x}{cmd:[}{it:i}{cmd:,.]}             {it:i}th row
	{it:x}{cmd:[.,}{it:j}{cmd:]}             {it:j}th column

	{it:x}{cmd:[}{it:i}{cmd:,]}              same as {it:x}[{it:i}{cmd:,.]}
	{it:x}{cmd:[,}{it:j}{cmd:]}              same as {it:x}{cmd:[.,}{it:j}{cmd:]}
	{hline 38}

{p 4 4 2}
Notes:

{p 8 11 2}
--
may be used on left or right side of equal sign

{p 14 17 2}
--
	{cmd:z = x[,j]}

{p 14 17 2}
--
	{cmd:x[,j] = z}

{p 8 11 2}
--
very fast



{title:3.  Specified rows and columns}

{p 4 4 2}
In {it:x}{cmd:[}{it:i}{cmd:,}{it:j}{cmd:]}, 
{it:i} 
and
{it:j} 
may be vectors

{p 8 11 2}
-- good style:

{p 14 17 2}
-- {it:i} a column

{p 14 17 2}
-- {it:j} a row

{p 11 11 2}
but it does not matter


{p 8 11 2}
-- elements may be repeated


{p 8 11 2}
-- may be used on left or right of equal sign


{p 8 11 2}
-- reasonably fast


{title:4.  Submatrices (range subscripts)}

{p 8 11 2}
--
{it:x}{cmd:[|}{it:i1}{cmd:,}{it:j1} {cmd:\} {it:i2}{cmd:,}{it:j2}{cmd:|]}
extracts the submatrix

{p 14 17 2}
--
with upper-left corner{bind:  }({it:i1},{it:j1})

{p 14 17 2}
--
with lower-right corner ({it:i2},{it:j2})


{p 8 11 2}
--
{it:x}{cmd:[|}{it:i1} {cmd:\} {it:j2}{cmd:|]} extracts subvector

{p 14 17 2}
-- 
from {it:i1} to {it:i2}

{p 14 17 2}
-- 
result is row if {it:x} is a row,
column if {it:x} is a column

{p 8 11 2}
--
very fast


{hline}
{bf:{view talk.smcl:Top}}