iteration help

[DanielleSavage]

Hello,

Does anyone know if there's any documentation on an abstraction for iterative algorithms to solve systems of equations?

Thanks,

D

[RichardJ · Accepted solution]

Look up "solve blocks" in the help.

[MikeArmstrong]

Why don't you post an example of your problem?

Mike

[DanielleSavage]

Mike,

This is an example:

x=sqrt((y-z)*2/r)

z= f*(L/D)*(x/2g)

f= something crazy with x in it

etc…(there are more equations with x in it)

So:

I say I need r to find x, but I need x to find z. I also need x to find f which is a part of finding z. So I guess a value for x, and then I use that value to find r and f. Then I go back and use the value I found for r and f to find x. I keep doing this until the guess and the calculated are the same.

Hopefully this helps,

D

[MikeArmstrong]

Richard is right. You could use a solve block and set up a series of simultaneous equations.

Mike

[MikeArmstrong]

Just tried to edit my post and the site wouldn't let me.

Was meant to say - Post the worksheet so someone can try set it up for you.

Mike

[DanielleSavage]

Indeed the help function is useful. There is a great discription of what I need to do.

Thanks,

Mike and Richard

[MikeArmstrong]

Sorry to sound negative, but threads like this are worthless to other forum members unless a worksheet with the problem and solution is posted.

If someone is having trouble with solve blocks and come across this thread I doubt it would be of much use, when it should yield a working example.

Mike

[RichardJ]

Put the equations in a solve block and use "Find" to find x, r, and f at the same time. Since you have 3 unknowns you will need 3 equations. If you have more than 3 there will, in general, be no exact solution. In that case you could use "minerr" instead of "Find" though, and it will find the values of x, r, and f that minimize the errors in the equations.

[MikeArmstrong]

& three guess values????

Mike

[RichardJ]

That would certainly help