回复： using newton raphsson zero finder

[049]

Dear all,

I'm trying to use Newton Raphson zero finder VI, but till now I can't get any result from it.. I want to know the proper way to feed it with an equation.. I need it to solve a Photovoltaic iterative equation

I= Iph - Io*(exp(V+I*Rs) - 1)  + (V+I*Rs)/Rp

I'm looking forward for your help

[altenbach]

As mentioned in the original thread, you need to help us too. 🙂

Could you give a bit more details and possibly attach your VI and some typical data?

[ttrr]

Hi,

You could specify the equation as a formula string, such as

10.0-1.0*(exp(2.0+x*15.0)-1)+(2.0+x*15.0)/20.0-x

where x is the unknown variable which **MUST NOT** be in captial letter. And, I suppose that

Iph = 10.0, Io = 1.0, V = 2.0, Rs = 1.5, Rp = 20.0

are known coefficients. You have to explicitly code those values in the formula string.

Starting from LabVIEW 2009, the Newton Raphson Zero Finder VI has a new instance for VI reference input. That is to say, you could create a VI to implement your function and pass the reference of that VI to the zero finder VI. Moreover, you can pass arbitrary values to your function VI. By using this way, it is able to solve the problem where you want to find zeros in a loop and the known coefficients are varied in each iteration.

[049]

Thanks a lot for your answer,  I do want to specify the equation into a formula string , but all my tries with converting the Formula into string never works and the result of the Zero is always NaN + there is an error message appears from the "Scan from String" function refering to invalid input.

would you please give an example of creating a formula string for the Newton ............ VI ?

[049]

I attached the try I made to convert the formula into string for the N-R zero finder

[altenbach]

Maybe this will help?

Also, you are reducing all your inputs to a single DBL. How is the subVI supposed to know all the variables?

Message Edited by altenbach on 08-20-2009 08:58 AM

[altenbach]

Also remember that array indices start with zero. Thus there is no element 6 for a size=6 array. The last one is index 5.

[ttrr · Accepted solution]

帖子被ttrr在 08-20-2009 08:14 PM

时编辑过了

[049]

thanks a lot !! , only How do you input the a,b,c,d... variables into the for loop ? I couldn't find this string table in my Labview 8.5 ... can you give me the right name of it ?

[RavensFan]

That is a string array.  Array container.  Drop a string constant into it.  Expand it.  Type in the values you want for each element