Posts: 1
Threads: 1
Joined: Jan 1970
I'm taking a first calculus course at Paris VI and i want to programm a piecewise function on the HP 48 calculator.
The function is :
F(x)= 3x if x<-5
= x/2 -5 if -5<x<0
= exp(x) if x>0
I programmed:
<< ---> X
<< CASE
' x<-5' THEN ' 3x' END
' -5< x < 0 ' THEN ' x/2 -5 ' END
' x > 0' THEN ' exp(x)' END
END
>>
>>
But i don't get the numeric result, only the algebraic expression corresponding to the input domain?
Posts: 909
Threads: 40
Joined: Jan 1970
Maybe you need to press "-> NUM"?
Posts: 25
Threads: 2
Joined: Jan 1970
> But i don't get the numeric result, only the algebraic expression
> corresponding to the input domain?
Just add EVAL after any algebraic expression you need to evaluate.
It looks like there is a test who needs to be re-written, too:
<< ---> X << CASE 'X < -5' THEN '3*X' EVAL END
'X > -5 AND X < 0' THEN 'X/2-5' EVAL END
'X > 0' THEN 'EXP(X)' EVAL END
END >>
>>
--
Posts: 4,027
Threads: 172
Joined: Aug 2005
Hi;
Just to know: does the final expression, when evaluated, return the expected result? If so, a single ->NUM after the last END is enough, because all possible CASEs return an algebraic expression. Say, you could try:
« -> X
« CASE
'X<-5' THEN '3*X' END
'X>-5 AND X<0' THEN 'X/2-5' END
'X>0' THEN 'EXP(X)' END
END ->NUM
»
»
(the ->NUM can also come between both » and »). If you wanna try an RPL solution (no need of a ->NUM adding):
« -> X
« CASE
X -5 < THEN X 3 * END
X -5 > X 0 < AND THEN X 2 / 5 - END
X 0 > THEN X EXP END
END
»
»
(I know you did not ask for it, but I am a compulsive RPL programmer... my shrink said so.)
Hope you have success.
Posts: 22
Threads: 1
Joined: Jan 1970
Hi Fernando,
Another way is this:
Type in:
'F(X)=IFTE(X<-5,3*X,IFTE(X>-5 AND X<0,X/2-5,EXP(X)))'
Then press left-shift STO (= Define)
Press VAR and you'll see the variable (function) F.
Type a value and press the softkey for F and this will be evaluated immediately.
Right-shift F will give you the program the HP48 has created as a result of the DEFinition.
IFTE = short IF THEN ELSE
Using this construction you can plot piecewise functions too.
Arnold