File Handling in formula node

Hello All,
I am trying to open a file and write some data to a file within the formula node. A declaration like
file *in;
produces this error:
Formula Node:undefined variable.
Error on line 1 is marked by a '#' character: "file# *out;"
How does one do file I/O operations within the formula node?
Thanks,
KB

Hello KB,
it seems you are trying to write a LabView program by
inserting C-code into a formula node... That's not the way it should be.
As far as I know there is no way to open a file inside the formula node. (It's a "formula" node!) So you have to open the file with LabView for reading and/or writing. Use your prefered subVi from the file palette. Perhaps you have to convert the data to a format suitable for your formula node (like string to U8-array).
In my experience it's better to use Labview-code instead of the formula node. In my programs a formula node was always slower than Labview code. So you should think about converting the C-style code to Labview.
Best regards,
GerdW
Best regards,
GerdW
CLAD, using 2009SP1 + LV2011SP1 + LV2014SP1 on WinXP+Win7+cRIO
Kudos are welcome

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Array Handling in Formula Node

I have attached a simple VI wherein I want to take an input array, look at its size and use the size of the input array as the size of the output array. The output array needs to be declared. I want to be able to use the size of the input array "N" as the size of the output array too. The size of the input array changes dynamically based on my simulation needs. I dont want to modify the size of the array in the declaration every time I change the array size in simulation.
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Attachments:
Array Handling in Formula node.vi ‏8 KB

AGovi wrote:
However I require to use complicated formulas such as
If a simple formula is easier in G, a complicated formula will also be easier in G.
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LabVIEW Champion . Do more with less code and in less time .

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Is it possible to have a calculation performed based on an equation stored in a string (read from a text file). I am guessing not because the equation would need be compiled but thought I would ask.

Hi,
it depends on how complex the equation is.
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If-then statement in formula node

**Note - The attached file shows the current block diagram.
I have a formula node inside a for loop. Inside the formula node I am trying to program the if-then statement:
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Attachments:
if-then_in_FN.jpg ‏18 KB

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I make a data analysis program, where the data consists of some million events and each event has e.g. 4 channels and 1-5 hits on each channel.
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Attachments:
LV script test.png ‏62 KB
LV script test.vi ‏18 KB

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LabVIEW Champion . Do more with less code and in less time .

How to handle unknown root node type when parsing?

Hello all, hoping someone knows how to accomplish this...
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     at com.bea.xbean.store.Root.autoTypedDocument(Root.java:394)
     at com.bea.xbean.store.Root.loadXml(Root.java:763)
     at com.bea.xbean.schema.SchemaTypeLoaderBase.parse(SchemaTypeLoaderBase.java:286)
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     at Test.main(Test.java:21)
Exception in thread "main"
So how do I generically handle parsing when I don't know what type of root node
I'm going to get?
Thanks,
Joe

Hello Joe -- You might try parsing the document as XmlObject (which your
schema-generated types extend). Then you could use an XmlCursor to discover
what the root element's local name is. Something like the following code
might be a way to do it. You could also simply re-parse the document after
discovering its root element name, but that would probably be more
expensive.
XmlObject xml = XmlObject.Factory.parse(mydoc.xml);
XmlCursor cursor = xml.newCursor();
cursor.toFirstContentToken();
if (cursor.getName().getLocalPart().equals("Research"))
// cast the XmlObject to your ResearchDocument type and use it.
else if (cursor.getName().getLocalPart().equals("Product"))
// cast the XmlObject to your ProductDocument type and use it.
cursor.dispose();
Steve
"Joe Celentano" <[email protected]> wrote in message
news:[email protected]..
>
Hello all, hoping someone knows how to accomplish this...
I'm trying to use XMLBeans to parse RIXML 2.0 documents. This schemaallows for
multiple root node types, so I don't know when I'm trying to parse a fileif the
root node is a Research node or a Product node, for example. If I try toinvoke
parse and there is a type mismatch I get the following error:
com.bea.xml.XmlException: D:\RIXML\V2TestDoc.xml:0: error: The document isnot
a Research@http://www.rixml.org/2002/6/RIXML: document element local name
mismatch
expected Researchgot Product
at com.bea.xbean.store.Root.verifyDocumentType(Root.java:472)
at com.bea.xbean.store.Root.autoTypedDocument(Root.java:394)
at com.bea.xbean.store.Root.loadXml(Root.java:763)
atcom.bea.xbean.schema.SchemaTypeLoaderBase.parse(SchemaTypeLoaderBase.java:28
6)
atcom.bea.xbean.schema.SchemaTypeLoaderBase.parse(SchemaTypeLoaderBase.java:22
4)
at org.rixml.x2002.x6.rixml.ResearchDocument$Factory.parse(Unknown Source)
at Test.main(Test.java:21)
Exception in thread "main"
So how do I generically handle parsing when I don't know what type of rootnode
I'm going to get?
Thanks,
Joe

Gamma function in formula node

I am running LabView V.6.1 and try to use the gamma function in a formula node.
According to the HELP text ''Formula Node and Expression Node Functions'', the syntax for the Gamma funtion is gamma(x), but this leads to the block diagram error ''Formula node: Undefined variable''.
Other functions (like exp(x), sqrt(x) etc.) work.
Thanks for helping.

Hi,
we ran into this one a little while ago. The help is a little misleading. The Gamma function actually only works with the Expression Nodes, and not the Formula nodes.
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Also refer to the following link for a bit more information :
http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RPAGEID=135&HOID=50650000000800000020540000&UCATEGORY_0=_49_%24_6_&UCATEGORY_S=0&USEARCHCONTEXT_QUESTION_0=%22Square%22+function+in+formula+node&USEARCHCONTEXT_QUESTION_S=0
it's a bit long winded, but be patient - the information is in there.
Hope that helps
S.
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"Square" function in formula node

The square(x) function in the formula node does not seem to work, can someone confirm, or give me some example syntax?
LabVIEW 6.1, Win2K
Certified LabVIEW Architect

Hi Nadav, Sacha and Martin
1. The Square Function is not Avilable in Base Package.
2. The Square Function will not work in the Formula node. There are differences in using the Formula Node and Mathematics Parser. Please Look at attached file in .rtf format. This is Just a Copy of LV6.1 Help
3. To Implement A Square(x) function Use "Eval Formula Node.vi" or Square(x) function as defined above.
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Good Luck!!
Mache
Good Luck!
Mache
Attachments:
Square_Function.vi ‏16 KB
Square_Fucntion_2.vi ‏26 KB
Differences_Between_the_Parser_in_the_Mathematics_VIs_and_the_Formula_Node.rtf ‏16 KB

Why do in-line conditional expressions work in Formula Node but not in 'Eval Formula Node.vi'?

'Eval Formula Node.vi' and a standard Formula node seem identical in most respects in terms of their functionality, however I'm stumped by the case of inline conditional expressions.
I'd like to read in a string in the syntax "(expr)?(expr)expr)" from a text file and recieve the output as a double.
The subVI seemed like the perfect tool since I was already using it to interpret a number of other calculations within the text file, however in this case the behavior is not as expected.
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Are there other features of the Formula Note not replicated by this VI? (so I can avoid them in future)?
For simplicity I've attached a little demo of the behavior.
I am currently working in 2010, which I know is getting on in years.
If the behavior is improved in later versions, that may be a good excuse to upgrade :-)
Thanks,
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Attachments:
Conditional Formula Node demo.vi ‏13 KB

.aCe. wrote:
Eval formula Node does not do any conditional expressions as far as I am aware.
That is right. It's a rather dirty hacked VI library to do some formula evalution and has many limitations in comparison to the Formula Node including no support for conditional operator as well as some others. In addition it can also error on some more complex bracketed expressions.
It is an old example VI that was never revisited and probably never will be as writing a new one from scratch would be easier. But considering that the Formula Node and Mathscript and other possibilities exist, this is not likely going to happen soon.
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CIT Engineering Netherlands
a division of Test & Measurement Solutions

Want to learn more about shift registers and formula nodes

I am new to Labview and have looked at the example files and help files regarding shift registers and formula nodes. I was hoping that someone has a simple and detailed VI expaining how each of them(shift registers and formula nodes) works.

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I included a simple example that illustrates what a shift register does. Requires Labview 7.1
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Attachments:
shift (LV7.1).vi ‏19 KB

How can I programatically perform a conditional formula in "Eval Formula Node"?

Okay, I'm stumped. I have an application where I need to evaluate a conditional programatically, and I can't do it with a Formula Node.
Basically, my user wants to be able to enter some formula which describes conditionals, such as "if this temperature goes above X degrees or this temp goes above Y degrees, then take a reading" kind of thing. Since the conditional will be saved in a file, the formula node needs to be dynamic.
I've used the "Eval Formula Node" before, which is built for this type of application...sort of. I tried it, but after trying in vain to get it to work properly, found out that it doesn't do boolean and conditionals in its parser, so it won't work.
Does anyone
have a good idea how to do this??

Why do you even want to use the formula node at all? I don't think you "can take a reading" (i.e. interact with hardware) inside a formula node anyway.
The formula node allows conditionals, see e.g. the example in the online help (image attached).
You could also use a case structure with seperate formula node in each case.
I highly prefer to skip the formula node and use wires instead. It will be more efficient and also much easier to debug. A formula node is not "in the true spirit of LabVIEW" ;-)
LabVIEW Champion . Do more with less code and in less time .
Attachments:
FormulaNode.gif ‏2 KB

File handling deprecated method - which one?

I have this code, it should basically use the lines of text in a file and use them to construct nodes in a JTree. The compilation error is that the class uses a deprecated method - so does anybody know what method is the problem and what I should use?
private void createNodes(DefaultMutableTreeNode top)
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   File theFile = new File("categories.txt");
try
DataInputStream din1 = new DataInputStream(new FileInputStream(theFile));
    //while (din1.available() !=0)
    while (true)
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If you compile with deprecation it will tell you specifically.
I think it is:
javac -deprecation ...
The only method from below that I think it could be is readLine() in DataInputStream...
If you are reading text...try:
BufferedReader br = new BufferedReader(new FileReader(theFile));
String topic;
while ((topic=br.readLine())!=null)
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br.close();

It crushes when the formula in a Formula Node is somewhat complicated.

I call outer Formula Node VIs using Call By Reference Node VI. This works well in general but for some VIs with a little complicated formulas. The system crushes while calling the VI repeatedly. In the attached files, Script1.vi goes well but Script0.vi doesn't. The difference between two is just that the expressions in the former are short (but equivalent essentially). Are there any rules or constraints here?
Attachments:
TestScript.zip ‏40 KB

Hi Randy,
Thanks for your answer.
I've raised one more question at the forum. I lastly attached a sample program for explaining the issue. I would greatly appreciate if you check the program at http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RPAGEID=135&HOID=5065000000080000008A6D0000&UCATEGORY_0=_49_%24_6_&UCATEGORY_S=0.
Michiro

Array index problem in formula node

dear friend
I'm trying to use formula node to solve a problem because I make this program using c at the begining.
It runs perfectly in turbo c, but somehow it doesn't work in the formula node.
I try to debug my source code, and I find that the formula node seems can't read the true value in
the array.
Here is the code in the formula node.
int32 i,j,k;
for ( i = 0 ; i < sopa; i++ )
j = 1;
ep[i][0] = pa[i];
ep[i][1] = np[ep[i][0]][0];
while ( ep[i][j-1] != exit )
  for ( k = 0 ; k < sonp ; k++ )
    if ( np[ep[i][j-1]][k] != -1 && (pc[ep[i][j-1]][ep[i][j]] + pc[ep[i][j]][exit] >= pc[ep[i][j-1]][np[ep[i][j-1]][k]] + pc[np[ep[i][j-1]][k]][exit] ) && (pc[ep[i][j-1]][np[ep[i][j-1]][k]] == org[ep[i][j-1]][np[ep[i][j-1]][k]] ))
      ep[i][j] = np[ep[i][j-1]][k];
  j++;
This is the part that I think the problem might be.
if ( np[ep[i][j-1]][k] != -1 && (pc[ep[i][j-1]][ep[i][j]] + pc[ep[i][j]][exit] >= pc[ep[i][j-1]][np[ep[i][j-1]][k]] + pc[np[ep[i][j-1]][k]][exit] ) && (pc[ep[i][j-1]][np[ep[i][j-1]][k]] == org[ep[i][j-1]][np[ep[i][j-1]][k]] ))
ep[i][j] = np[ep[i][j-1]][k];
I state that "np[ep[i][j-1]][k] != -1" but I do get the value -1 in the array "ep".
Could someone tell me why I get -1 in the array?
I hope I can finally do it all by labview not using formula node,but array like "pc[ep[i][j-1]][np[ep[i][j-1]][k]] "
seems very hard to wire in labview. Could someone give me some good advices of doing this?
Thanks for your help

altenbach 已寫:
normanshi wrote:
ep[i][0] = pa[i];                                          (A)
ep[i][1] = np[ep[i][0]][0];                            (B)
...    if ( np[ep[i][j-1]][k] != -1 && ... )          (C)
      ep[i][j] = np[ep[i][j-1]][k];                       (D)
I state that "np[ep[i][j-1]][k] != -1" but I do get the value -1 in the array "ep".
Could someone tell me why I get -1 in the array?
I hope I can finally do it all by labview not using formula node,but array like "pc[ep[i][j-1]][np[ep[i][j-1]][k]] "
seems very hard to wire in labview. Could someone give me some good advices of doing this?
There are many possible scenarios to get a -1 in the ep output. For example if the -1 gets already written in step (A) or (B) at a certain index, and that index does not get overwritten in step (D). You are indexing all over the place! Is there some bounds checking on the array contents? What are typical inputs and array sizes?
I'm sure about that the -1 doesn't get already written in step (A) or (B) because ep[i][0] and ep[i][1] is fine. What really makes me confuse is that sometimes ep array has the value like this.
That means it does overwritten some value in step (D). The -1 should never be written into it because I have already state that np[ep[i][j-1]][k] != -1. Somehow I still get -1,and this is really strange! I'm indexing all over the place becuase I can't figure out a better way to achieve my requirement.
I think I should briefly tell you what I'm trying to do. In this program,I input some values which means the distance from one point to another. Then I use floyd's all pairs shortest-path algorithm to find all the shortest distance. Finally I want to find out the "shortest path". I mean like from point 4 to point 0,the shortest path might be like 4 -> 2 -> 1 -> 0, and what the formula node part do is trying to find out this "shortest path". Maybe you can give me some better advice of doing this, I have been thinking a better way to do it for about two months. I think I'm really not good at this.
I try to do it all by labview ,but again I get a strange problem. This time the ep[i][j-1] doesn't get the correct value. In the first time i=0 j-1=0 ep[i][j-1] = 1,but the second time i = 0 j-1 = 1 ep[i][j-1] = 0. This makes the "ep[i][j-1]!=exit" get the incorrect boolean value. The ep[i][j-1] should be 2,not 0. I try to use highlight to find if I make any mistake, but I can't one.This is the input and I put the labview program in attached file (temp4.vi).
Could you help me find out why this happened?
Thanks for your help altenbach!
由 normanshi 在 08-19-2006 10:06 PM 上編輯的訊息
Attachments:
temp4.vi ‏191 KB
ep.jpg ‏10 KB
input.jpg ‏9 KB

Array in formula node

Hello everyone,
I am new in labview. I would like to display the coherence function with the correct frequency scale. For instance, I want it to be as follow: FreqAxis = 0:Fs/2/(N+1):Fs/2. where Fs is the sampling frequency and N the number of sample. I am trying to write using Formula node, but it is not working.
Thanks for your time and your help.
Axel

Thanks again for your comments and your time .
I have attached the .vi file and a screen-shot of the expected result (cohere2.png).
Cheers
Axel
Attachments:
Code_frequency.vi ‏531 KB
cohere2.PNG ‏17 KB

File Handling in formula node

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