| Author |
Message |
sisseck
Joined: 31 Oct 2007
Posts: 2
|
 Posted: October 31, 2007 4:32 AM Post subject: More working with multiple answers |
 |
|
| Hi i just read the topic about multiple answers and the part() command works great. But i am working on a program where the solve() function gives multiple x and y values. The really tricky part is that the number of solutions are not constant. Anyone know how to get around this problem? |
|
| Back to top |
|
 |
mellamokb
Joined: 10 May 2007
Posts: 100
|
| Posted: October 31, 2007 10:00 AM Post subject: |
|
|
Hi sisseck,
Welcome to TI-89.org forums.
It's really hard to help you with your problem without some sort of example to go off of. There are very many ways to parse information if you have criteria. For instance, you could use the "part(" function in a loop to continuously retrieve values of x and y until a certain criteria is met, like the part function returns a number instead of an equation. If you could give a concrete example portraying the complexity of your equations you are solving, then I could suggest some better possibilities for you.
Hope this helps!
~ mellamokb |
|
| Back to top |
|
|
sisseck
Joined: 31 Oct 2007
Posts: 2
|
| Posted: October 31, 2007 1:10 PM Post subject: min max and saddelpoints |
|
|
| The equations im working on are 3d grafs z(x,y)=x^4+16xy+y^4 for instance. up till now the program i have written can hande it as long as there is only 1 max. min. or saddel point. I'm pretty sure that the part command will do the trick, but still need to figure the finer points of the programming out. |
|
| Back to top |
|
|
mellamokb
Joined: 10 May 2007
Posts: 100
|
| Posted: November 5, 2007 11:34 AM Post subject: |
|
|
sisseck,
Here is an example of what I meant in my previous post. Suppose you solved an equation and got the following result:
| Code: |
x=5 and y=19 or x=3 and y=22 or x=6 and y=10
|
Clearly, there are three solutions to x and y that you want out of this expression. Also, actual solutions are separated by the word "or". If you use the part function on this expression, it will separate pieces around the word "or", which is pretty convenient:
| Code: |
part(x=5 and y=19 or x=3 and y=22 or x=6 and y=10, 0)
"or"
part(x=5 and y=19 or x=3 and y=22 or x=6 and y=10, 1)
x=5 and y=19
part(x=5 and y=19 or x=3 and y=22 or x=6 and y=10, 2)
x=3 and y=22 or x=6 and y=10
|
So a short function to get all the solutions and return them as a 2xn matrix might go something like this (assuming the solution expression like "x=5 and y=19 or x=3 and y=22 or x=6 and y=10" is passed as the argument, e):
| Code: |
parsesol(e)
Func
Local i,s,lx,ly
NewList(1)->lx
NewList(1)->ly
1->i
While part(e,0)="or"
part(e,1)->s
part(e,2)->e
part(part(s,1),2)->lx[i]
part(part(s,2),2)->ly[i]
i+1->i
EndWhile
part(part(e,1),2)->lx[i]
part(part(e,2),2)->ly[i]
Return {lx,ly}
EndFunc
|
Example usage:
| Code: |
parsesol(x=5 and y=19 or x=3 and y=22 or x=6 and y=10)
[[3,5,6][22,19,10]]
|
You should be able to get the general idea from the function I've written. You could also use a program if you wanted instead of a function (programs allow input/output, functions don't, but can return values to the home screen, unlike programs). You should be able to fine-tune the idea using different comparisons and combinations of the part( function for your particular situation.
Another interesting built-in function you might look at is the zeros( function, which will find all zeros of an expression and return them as a list rather than "x=5 or x=6 or x=7 or ...", which might be easier to work with. Here is an example usage to compare the two:
| Code: |
Solve(x^3-7x=-6,x)
x=-3 or x=1 or x=2
Zeros(x^3-7x+6,x)
{-3,1,2}
|
Hope this helps!
~ mellamokb |
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
Saphic 1.5 // Theme created by Sopel
|
|
