Texas Instruments TITANIUM TI-89 - Manual (Page 807)

Appendix A: Functions and Instructions 807
Define CATALOG
Define funcName ( arg1Name, arg2Name, ... ) =
expression
Creates funcName as a user-defined function. You
then can use funcName() , just as you use built-in
functions . The function evaluates expression using
the supplied arguments and returns the result.
funcName cannot be the name of a system
variable or built-in function.
The argument names are placeholders; you
should not use those same names as arguments
when you use the function.
Note: This form of Define is equivalent to
executing the expression:
expression !funcName(arg1Name,arg2Name) .
This command also can be used to define simple
variables; for example,
Define a=3 .
Define g(x,y)=2xì 3y ¸ Done
g(1,2) ¸ ë 4
1! a:2! b:g(a,b) ¸ ë 4
Define h(x)=when(x<2,2x-3, ë 2x+3)
¸ Done
h(л 3) ¸ л 9
h(4) ¸ ë 5
Define eigenvl(a)=
cZeros(det(identity(dim(a)
[1])-xù a),x) ¸ Done
eigenvl([л 1,2;4,3]) ¸
{ 2ш 3 - 1
11
л (2ш 3 + 1)
11
}
Define funcName ( arg1Name, arg2Name, ... ) = Func
block
EndFunc
Is identical to the previous form of Define ,
except that in this form, the user-defined function
funcName() can execute a block of multiple
statements.
block can be either a single statement or a series
of statements separated with the “:” character.
block also can include expressions and
instructions (such as If , Then , Else , and For ).
This allows the function funcName() to use the
Return instruction to return a specific result.
Note: It is usually easier to author and edit this
form of Function in the program editor rather
than on the entry line.
Define g(x,y)=Func:If x>y Then
:Return x:Else:Return y:EndIf
:EndFunc ¸ Done
g(3,ë 7) ¸ 3
Define progName ( arg1Name, arg2Name, ... ) = Prgm
block
EndPrgm
Creates progName as a program or subprogram,
but cannot return a result using Return . Can
execute a block of multiple statements.
block can be either a single statement or a series
of statements separated with the “:” character.
block also can include expressions and
instructions (such as If , Then , Else , and For )
without restrictions.
Note: It is usually easier to author and edit a
program block in the Program Editor rather than
on the entry line.
Define listinpt()=prgm:Local
n,i,str1,num:InputStr "Enter name of
list",str1:Input "No. of
elements",n:For i,1,n,1:Input
"element "&string(i),num:
num! #str1[i]:EndFor:EndPrgm ¸
Done
listinpt() ¸ Enter name of list
DelFold CATALOG
DelFold folderName1 [, folderName2 ] [, folderName3 ] ...
Deletes user-defined folders with the names
folderName1 , folderName2, etc. An error message is
displayed if the folders contain any variables.
Note: You cannot delete the main folder.
NewFold games ¸ Done
(creates the folder games )
DelFold games ¸ Done
(deletes the folder games )