MaplePrimes - answers and comments on Question, Can someone please help me on this problem?

RE: Can someone please help me on this problem?

Ken Lin — Wed, 25 Feb 2009 22:35:33 Z

To make your program more readable for help in the future, you should use some indents. Allow me to make some changes in your program which I listed below.

f:=x->x^3+6*x^2-11*x-10:
A:=1:
M:=0.0001:
E:=M+1:

while (A<>n) do
A:=readstat("Would You Like To Find Another Root?[y/n](n to quit)"):

   if A=y then
      B:=readstat(`Initial Value One?`):
      C:=readstat(`Initial Value Two?`):
      if sign(f(B)) = sign(f(C)) then
           printf("No Roots In The Interval %a",[B,C]);
      else
           while E>M do
               d:=evalf((B+C)/2):
               #print('d'=d):
               print('f'(d)=f(d)):
               if   f(d)>0 and f(d)<f(C) then
                      C:=d;
                      E:=abs(f(d)):
               elif f(d)>0 and f(d)<f(B) then
                      B:=d:
                      E:=(abs(f(d))):
               elif f(d)<0 and f(d)>f(B) then
                      B:=d;
                      E:=(abs(f(d))):
               elif f(d)<0 and f(d)>f(C) then
                      C:=d:
                      E:=(abs(f(d))):
               elif f(d)=0                     then
                      E:=0:
               end if:
           end do:
      end if:
      print(sol=evalf(d));
   end if:
end do:

Ken.Lin @ Taiwan

while E > M

Robert Israel — Thu, 26 Feb 2009 02:00:13 Z

In the "while E > M do ...", E is supposed to be the absolute value of f at the last point
computed. When that falls below M = 0.001, you stop your iteration. Then you go and ask for a new A, B and C, but E is still the same (the value that made you stop before), so your while loop stops before it starts. I think you'll want to put your

E := M + 1;

some place after the

while (A <> n) do

and before the

while E > M do

It works

Jabz — Thu, 26 Feb 2009 03:11:42 Z

Thank you so much for your help. I have been stuck on this for about a week i just could not find the problem.

Thank you very much

Thanx

Jabz — Thu, 26 Feb 2009 00:15:21 Z

Hi I'm really new to programming so i dont really know much about the layout and that but thank you for showing me the correct way.

The problem that i had still exists. I tried looking for the other roots but it just gives me the previous any soln?

Re: Thanx

Ken Lin — Thu, 26 Feb 2009 07:12:46 Z

I am glad to hear from you that everything is going right. Also thanks to Robert Israel who helps find bugs in your program. For your reference, you may use the if...elif...else... structure in the future for a substitute of the "case" control structure in other modern programming language. By the way, you may also use the Maplets[] package(library) for a better GUI. I list an example in the next line which refines the "readstat("Would You Like To Find Another Root?[y/n](n to quit)")" in your original program.

> Maplets[Examples][Confirm]("Would You Like To Find Another Root?");

Best regards,

Ken.Lin @ Taiwan

hi kin

Jabz — Tue, 03 Mar 2009 06:12:38 Z

Hi kin

I tried to implement the above for my program bt it comes up with an error saying that `else unexpected`.

The parts in italics are the new changes to the above program the rest is the same.

A:=1:
M:=0.0001:
while (A<>false) do

   A:=Maplets[Examples][Confirm]( "Would You Like To Find Another Root?" ):
     if A=true then
      B:=readstat(`Initial Value One?`):
      C:=readstat(`Initial Value Two?`):

    else
       NULL;
else
    if B >= C then
          printf("Incorrect Values %a",[a,b]);
   else ..........

P.s when i delete the else it works but not properly.