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{SECT 0 {PARA 0 "" 0 "" {TEXT -1 0 "" }}{SECT 0 {PARA 0 "" 0 "" {TEXT 
26 7 "Advice:" }{TEXT -1 21 " Last name evaluation" }}{PARA 0 "" 0 "" 
{TEXT -1 0 "" }}{PARA 0 "" 0 "" {TEXT -1 204 "Normally, when you enter
 an expression it is evaluated completely.  If your expression contain
s a variable that has a value, the variable is replaced by that value;
 if it contains a function call such as " }{MPLTEXT 0 21 4 "f(x)" }
{TEXT -1 8 ", where " }{MPLTEXT 0 21 1 "f" }{TEXT -1 76 " is a procedu
re or function, then this is replaced by the value returned by " }
{MPLTEXT 0 21 1 "f" }{TEXT -1 15 " with argument " }{MPLTEXT 0 21 1 "x
" }{TEXT -1 557 ".  And if those values in turn contain variables or f
unction calls, they are also evaluated.  Eventually (we hope) Maple ob
tains a form that does not require any further evaluation, and this is
 what it returns to us.  However, certain types of object have special
 evaluation rules.  In particular, tables, arrays (including vectors a
nd matrices) and procedures use last name evaluation.  This means that
 if the result of one level of evaluation of a name would be a table, \+
array or procedure, then the chain of evaluation stops with that name.
  For example:" }}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 19 "T:= array(
[a,b,c]);" }}{PARA 11 "" 1 "" {XPPMATH 20 "6#>%\"TG-%'VECTORG6#7%%\"aG
%\"bG%\"cG" }}}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 6 "S:= T;" }}
{PARA 11 "" 1 "" {XPPMATH 20 "6#>%\"SG%\"TG" }}}{EXCHG {PARA 0 "> " 0 
"" {MPLTEXT 1 0 2 "S;" }}{PARA 11 "" 1 "" {XPPMATH 20 "6#%\"TG" }}}
{PARA 0 "" 0 "" {TEXT -1 24 "In the first statement, " }{MPLTEXT 0 21 
1 "T" }{TEXT -1 46 " is assigned a value which is an array.  Then " }
{MPLTEXT 0 21 1 "S" }{TEXT -1 23 " is assigned the value " }{MPLTEXT 
0 21 1 "T" }{TEXT -1 1 "." }{TEXT -1 16 "  Evaluation of " }{MPLTEXT 
0 21 1 "T" }{TEXT -1 63 " stops at the name, rather than going all the
 way to the array " }{MPLTEXT 0 21 7 "[1,2,3]" }{TEXT -1 7 ".  For " }
{MPLTEXT 0 21 1 "S" }{TEXT -1 44 " there is one level of evaluation, y
ielding " }{MPLTEXT 0 21 1 "T" }{TEXT -1 57 ", but again evaluation st
ops there.  If you want the next" }}{PARA 0 "" 0 "" {TEXT -1 63 "level
 of evaluation, the table or array structure, you can use " }{MPLTEXT 
0 21 4 "eval" }{TEXT -1 1 ":" }}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 
8 "eval(S);" }}{PARA 11 "" 1 "" {XPPMATH 20 "6#-%'VECTORG6#7%%\"aG%\"b
G%\"cG" }}}{PARA 0 "" 0 "" {TEXT -1 118 "However, even this is not ful
l evaluation, as the entries of this array were not evaluated.  For th
at you need to map " }{MPLTEXT 0 21 4 "eval" }{TEXT -1 6 " into " }
{MPLTEXT 0 21 1 "S" }{TEXT -1 1 ":" }}{EXCHG {PARA 0 "> " 0 "" 
{MPLTEXT 1 0 26 "b:= a: a:= sin(x): x:= Pi:" }}}{EXCHG {PARA 0 "> " 0 
"" {MPLTEXT 1 0 8 "eval(S);" }}{PARA 11 "" 1 "" {XPPMATH 20 "6#-%'VECT
ORG6#7%%\"aG%\"bG%\"cG" }}}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 12 "m
ap(eval,S);" }}{PARA 11 "" 1 "" {XPPMATH 20 "6#-%'VECTORG6#7%\"\"!F'%
\"cG" }}}{PARA 0 "" 0 "" {TEXT -1 244 "Last-name evaluation is usually
 not a problem, and can have significant benefits in efficiency by avo
iding the copying of large tables or arrays.  However, there are some \+
points to watch out for.  One is that at first glance it may appear th
at " }{MPLTEXT 0 21 1 "T" }{TEXT -1 42 " has not been assigned a value
.  Even the " }{MPLTEXT 0 21 8 "whattype" }{TEXT -1 29 " function does
 not help here:" }}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 12 "whattype(
T);" }}{PARA 11 "" 1 "" {XPPMATH 20 "6#%'stringG" }}}{PARA 0 "" 0 "" 
{TEXT -1 21 "Instead, you can use " }{MPLTEXT 0 21 8 "assigned" }
{TEXT -1 31 ". Of course you could also use " }{MPLTEXT 0 21 7 "eval(T
)" }{TEXT -1 1 "." }}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 12 "assigne
d(T);" }}{PARA 11 "" 1 "" {XPPMATH 20 "6#%%trueG" }}}{EXCHG {PARA 0 ">
 " 0 "" {MPLTEXT 1 0 18 "whattype(eval(T));" }}{PARA 11 "" 1 "" 
{XPPMATH 20 "6#%&arrayG" }}}{PARA 0 "" 0 "" {TEXT -1 31 "Another commo
n problem is that " }{MPLTEXT 0 21 4 "subs" }{TEXT -1 108 " will not s
ee the table, array or procedure structure, but only the name.  Again,
 you can fix this by using " }{MPLTEXT 0 21 4 "eval" }{TEXT -1 1 "." }
}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 13 "subs(c=4, S);" }}{PARA 11 "
" 1 "" {XPPMATH 20 "6#%\"TG" }}}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 
19 "subs(c=4, eval(S));" }}{PARA 11 "" 1 "" {XPPMATH 20 "6#-%'VECTORG6
#7%%\"aG%\"bG\"\"%" }}}}{PARA 3 "" 0 "" {TEXT -1 0 "" }}{SECT 0 {PARA 
0 "" 0 "" {TEXT 26 9 "See also:" }{TEXT -1 1 " " }{HYPERLNK 17 "array
" 2 "array" "" }{TEXT -1 2 ", " }{HYPERLNK 17 "assigned" 2 "assigned" 
"" }{TEXT -1 2 ", " }{HYPERLNK 17 "eval" 2 "eval" "" }{TEXT -1 2 ", " 
}{HYPERLNK 17 "procedure" 2 "procedure" "" }{TEXT -1 2 ", " }
{HYPERLNK 17 "table" 2 "table" "" }}}{PARA 0 "" 0 "" {TEXT -1 0 "" }}
{SECT 0 {PARA 0 "" 0 "" {TEXT 26 24 "Maple Advisor Database, " }{TEXT 
-1 15 " R. Israel 1997" }}}}{MARK "2 0" 0 }{VIEWOPTS 1 1 0 1 1 1803 }