Formula node related VIs

I am looking for the following VIs for LabVIEW 7.0, does anyone have these files? Thanks.
Eval Formula node.vi
Parse Formula Node.vi
Eval Parsed Formula Node.vi

They should be in the "Analyze..Math..Formula" palette.
If they are not there, it could mean that you only have LabVIEW base. In this case you would need to upgrade to LabVIEW full or higher.
LabVIEW Champion . Do more with less code and in less time .

Similar Messages

Report of an apparent formula node casting bug

The attached LLB contains a vi (casting vi.vi) that causes LabVIEW to crash on my installation (6.02, Windows 2000). The crash is apparently related to a problem with automatic type-casting after a formula node, and inside a VI. The attached VIs were constructed from scratch to duplicate the crash, so it's not a corrupted file problem. Having isolated the problem this far, I can easily work around it; but I thought I should also report the issue, since I don't find it on your web site after a trying couple of different search strategies.
Attachments:
cast_failure.llb ‏23 KB

It seems the problem has been fixed: It does not crash under LabVIEW 6.1 or LabVIEW 7. (I can reproduce the crash under LabVIEW 6).
LabVIEW Champion . Do more with less code and in less time .

"Eval Parsed Formula Node VI" does not return outputs in predefined order

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.
I would like the user to select different expressions of these channels to give coordinates to plot in a 2D histogram (increment a bin in Intensity Graph), e.g. for some experiment you want to show x=ch1-ch2; y=ch1+ch2+ch3+ch4; while in another experiment you want x=ch1-123; y=123-ch2;
There are other VIs that use static LabView-code for the normal things, but now after a few years of adding to this program I find that it would be quite good with a general plotter and let the user specify simple expressions like this. Also with the "normal" static plots, there is a need to filter out bad data and then it would be much simpler both to program and use if you could write text expressions with boolean logic to combine multiple filters. Making a LabView code and GUI that allows AND/OR/parenthesis combinations of expressions will be quite an effort and not very reusable.
So, with the above motivation, I hope you see that it would make sense to have a useable string formula evaluator in LabView. I find some info about MathScript's user-defineable functions, but haven't managed to get MathScript working in LV2010 yet (maybe some licensing or installation issues, I think I had it in 8.6). But I think it would be possible to do most of what I want for the display-part (not the filtering) with the simpler Eval/Parse Formula Node VIs and suitable use of the limited variable name space. So I started testing, and found a quite annoying issue with how the evaulator works.
To the parser, you are expected to send an array of output variable names. But then it ignores this array, and returns one output per assignment/semicolon in the formula, in the order of the formula text. Since the static parts of my program need to know what the output values mean (which of them is x and which is y), I would have to rely on the user not using any intermediate variable and defining x before y. The attached screenshot demonstrates the problem, and also that it has been solved by NI statff in the "Eval Formula Node VI" which does the appropriate array-searching to extract only the pre-defined outputs, in their expected order. But using that VI is about 100 times as slow, I need to pre-compile the formula and then only use the evaulator in the loop that runs over a million events.
I don't know if I'll take the time to make my own tweks to the parsing stage (e.g. preparation of array-mapping to not have to repeat the search or maybe hacking the output list generated by the parser) or if I'll have to make it in a static Formula Node in the block-diagram (which supports more functions), so that the user has to run with development environment and stop the program to change the plotting function. But I wanted to share this trouble with you, in hope of improvments in future LabView versions or ideas from other people on how I could accomplish my aim. I have MATLAB-formula node possibility too, but is far as I have seen the only place the user could update the formula would then be in a separate .m file, which is re-read only when typing "clear functions" in the Matlab console window. (Having this window is also an annoyance, and perhaps the performance of calling Matlab in every iteration is not great.)
Besides this issue, it also seems very strange there is virtually no support for conditional expressions or operators in Formula Node evaulated formulas (called Mathematics VIs in the documentation). Maybe using (1+sign(a-b))/2 you can build something that is 0 when a<b and 1 when a>b, but it is not user friendly! Would it really be diffcult to add a function like iif(condition, return_value_if_true, return_value_if_false) to replace the unsupported "condition ? if_true : if_false" operator? Would it really be difficult to add support for the < <= >= > == || && operators? Although compiled to an assemply language, this can't exactly be difficult for a CPU.
Attachments:
LV script test.png ‏62 KB
LV script test.vi ‏18 KB

(1) You can put any kind of code inside an event structure with the limitation that it should be able to complete quickly and without user interaction. For example a while loop for a newton-raphson method is fine, but an interactive while loop where the stop condition depends on user iteraction is not recommended. By default, event structures lock the front panel until the event completes, so you would not even be able to stop it.
(2) Yes, you can do all that. LabVIEW has no limitation as a programming language. Use shift registers to hold data and state information, the manipulate the contents as needed.
(3) I would recommend to use plain LabVIEW primitives instead of formula nodes. Show us your code so we can better see what it's all about. Obviously you have a mismatch betweeen scalars and arrays. It is impossible from the given information where the problem is.
(4) Yes, look inside the nonlinear curve fit VI (you can open it an inspect the code!). One of the subVIs does exactly that. Just supply your model VI.
LabVIEW Champion . Do more with less code and in less time .

String array into formula node

Hello,
I am taking data from SQL, I am getting multiple rows of data for many different devices. I would like to wire the data into a formula node so I can sepearate and sort via script. However, I am getting an error for "Polymorphic terminal cannot accept this data type". Is there a work around? Can I not wire in a string array to a formula node.
/r
Travo

There are lots of basic string VIs that you can use to parse the string and separate out the individual fields. I would recommend "programming" your application using script nodes. Use the native language. LabVIEW is a fully functional and capable programming language.
Mark Yedinak
"Does anyone know where the love of God goes when the waves turn the minutes to hours?"
Wreck of the Edmund Fitzgerald - Gordon Lightfoot

How to change content in the formula node of the current vi

Actually I want to give formula with array index.
My formula p=a[0]-30; But i couldnot give array index in the formula expression..
Please help me in this issue.

Muthu92 wrote:
Thank you for your reply. It is very useful for me. But i can't give conditional operator in that operator. It is showing error.
My Test cases
A[0]+A[1]>150
A[31]-50 <100.
If those are your exact statements, then they don't make sense in a formula node. You have to use them in an if-statement or some other type of control logic. This mimics text-based programming languages such as C... See here for instructions on formula node syntax: http://zone.ni.com/reference/en-XX/help/371361G-01/lvhowto/formula_node_syntax/
For instance, you COULD say something like:
**In this example, let A[0] == x, A[1] == y, A[31] == z**
if(x+y>150)
/* do something if this is true */
else if(z-50 < 100)
/* do something else */
EDIT:
It should also be noted that Variable Names MUST be lowercase!! I just discovered this
EDIT2:
I stand corrected. After trying to create an example and digging through the LabVIEW Help, I stumbled across this:
Differences between the Parser in the Mathematics VIs and the Formula Node
The parser in the Mathematics VIs supports all elements that Formula Nodes support with the following exceptions:
Variables—Only a, a0, ..., a9, ... z, z0, ..., z9, are valid.
Logical, conditional, inequality, equality—?:,, &&, !=, ==, <, >, <=, and >= are not valid.
Functions—atan2, max, min, mod, pow, rem, and sizeOfDim are not valid. You can use these functions in a Formula Node or use their corresponding LabVIEW functions.
So it DOES NOT seem like Eval Formula Node can do conditionals like you want. I would just implement them using a LabVIEW based algorithm after all. Trying to out smart the formula nodes to avoid simple LabVIEW code is just too much of a hassle
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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.
Go to the labview help file, and search for "Differences Between the Parser in the Mathematics VIs and the Formula Node "
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.
// it takes almost no time to rate an answer

Functions in Formula Node

Hello:
I have written a simple formula node in the VI in annex. It uses two functions that should be called for R, G and B. Because I do not know how to implement functions (the way I implement C functions) I had to repeat 3 times the same code (for R, G and B) which makes the code not so readable and maybe I loose on performances? Could you correct the formula node by implementing functions, please? I was not able to find this tip in the various documentation that I have nor on the net. Thank you very much in advance,
Chris
Attachments:
myRGBtoLAB.vi ‏32 KB

Wow Chris!
That is one impressive formula node! In terms of computational efficiency, I wouldn't expect there to be a lot of difference between the formula node and separate VIs. Stll, I have attached two sub VIs that I think implement the two repeated areas of the formula node code.
Something to do though is change the type of all the outputs to doubles. The calculation is being done in double precision anyway, so you might as well preserve it. Also, the single frame sequence around the whole thing isn't performing any function so it can be deleted.
As far as readability goes, remember that readability (like beauty) is in the eye of the beholder. If you can read the code and know intuitively what it does, I wouldn't worry too much about it...
Mike...
Certified Professional Instructor
Certified LabVIEW Architect
LabVIEW Champion
"... after all, He's not a tame lion..."
Be thinking ahead and mark your dance card for NI Week 2015 now: TS 6139 - Object Oriented First Steps
Attachments:
n_to_n1.vi ‏22 KB
the_other_calculation.vi ‏25 KB

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

Atan2 equivalent in a Formula Node?

Does anyone have an atan2 (2-input inverse arctangent) equivalent for use in a Formula Node? I was surprised to see that such a common function wasn't supported in Formula Nodes. Without it, my easily readable Formula Node equations get junked and become a nightmare of LabVIEW math symbols. Is there a way to call the atan2 VI (or any other VI for that matter) from within a Formula Node?

Hello,
You are correct, this function is not supported in Formula Nodes, and there is not a way to call VIs from formula nodes. However, the below solution might be what you need:
Is this the correct definition of atan2:
if y = atan2(a,b), then tan(y) = (a/b)
If so, could we define a and b, and use the formula node function atan(a/b)? This may not be the most elegant solution, but it seems like it would do the trick with minimal headache. I attached a VI showing this idea.
Hope this helps!
Liz Fausak
National Instruments
Attachments:
atan2FNode.vi ‏10 KB
61atan2FNode.vi ‏10 KB
60atan2FNode.vi ‏8 KB

Array output from formula node

How to get an array output from the formula node.I am trying to use a for loop inside the formula node and want an array output.

You cannot place a For or While Loop inside the formula node.
Here is what the Help Description says about the syntax inside the Formula Node:
Formula Node
Evaluates mathematical formulas and expressions similar to C on the block diagram. The following built-in functions are allowed in formulas: abs, acos, acosh, asin, asinh, atan, atan2, atanh, ceil, cos, cosh, cot, csc, exp, expm1, floor, getexp, getman, int, intrz, ln, lnp1, log, log2, max, min, mod, pow, rand, rem, sec, sign, sin, sinc, sinh, sizeOfDim, sqrt, tan, tanh. There are some differences between the parser in the Mathematics VIs and the Formula Node.
Place on the block diagram
Find on the Functions palette
Refer to Creating Formula Nodes and Formula Node Syntax for more information about the Formula Node and the Formula Node syntax.
Note The Formula Node accepts only the period (.) as a decimal separator. The node does not recognize localized decimal separators.
<SCRIPT type=text/javascript>if (typeof(writeVarRefs)=="function"){writeVarRefs("763");}</SCRIPT>
<SCRIPT type=text/javascript> if(typeof(lvrthelp763) != "undefined"){document.writeln(lvrthelp763)}</SCRIPT>
<SCRIPT type=text/javascript> if(typeof(lvfpga763) != "undefined"){document.writeln(lvfpga763)}</SCRIPT>
<SCRIPT type=text/javascript> if(typeof(lvemb763) != "undefined"){document.writeln(lvemb763)}</SCRIPT>
<SCRIPT type=text/javascript> if(typeof(lvpdahelp763) != "undefined"){document.writeln(lvpdahelp763)}</SCRIPT>
<SCRIPT type=text/javascript> if(typeof(lvtpchelp763) != "undefined"){document.writeln(lvtpchelp763)}</SCRIPT>
<SCRIPT type=text/javascript> if(typeof(lvblackfin763) != "undefined"){document.writeln(lvblackfin763)}</SCRIPT>
<SCRIPT type=text/javascript> if(typeof(lvdsp763) != "undefined"){document.writeln(lvdsp763)}</SCRIPT>
Example
Refer to the Create Function with Formula Node VI in the labview\examples\general\structs.llb for an example of using the Formula Node.

Sine square function in formula node

Hello
I need to generate a function
I = Iz * sin^2(B)
where B = (pi/2)*(V/70)
Iz = 0, 0.1, 0.2, 0.3 ... 1.0
V = 1,2,3 ,4...135
I tried to do thi sin formula node. but cud not get it.
See attchment.
Nghtcwrlr
********************Kudos are alwayzz Welcome !! ******************
Attachments:
Sine square in formulanode.vi ‏18 KB

This will not work. B has 105 elements, and IZ has only 10. B and IZ must have the same numers of elements. And you should perhaps use a for loop not a formula node
Besides which, my opinion is that Express VIs Carthage must be destroyed deleted
(Sorry no Labview "brag list" so far)

Complex in Formula Node

I need to enter the following formula (j-imaginary 1) in Formula Node
x1=1/kr - j/(kr*kr) - 1/(kr*kr*kr);
x2=1/(kr*kr) - j/(kr*kr*kr);
Further I need to receive y = x1*conjugate(x1) + x2*conjugate(x2).
I do not know, how it is necessary to designate complex x1 and x2 in Formula Node and how to program conjugate. Help me, please!
Solved!
Go to Solution.
Attachments:
Formula.vi ‏9 KB

Formula node do not support complex numbers. But a Mathscript node do. But I am not sure you find Mathscript node in LV 7.1. But I think you are making things to complex. You do not need a formula node
Edit: Upsk made an error in the calculation, but it is fixed now
Message Edited by t06afre on 03-07-2009 12:03 PM
Besides which, my opinion is that Express VIs Carthage must be destroyed deleted
(Sorry no Labview "brag list" so far)
Attachments:
sample.vi ‏22 KB

Formula node forbid to run VI when undefined variable is used

On all LabVIEW version, we can use Formula node to evaluate mathematical formulas.
We can define input and output variable freely and calculate using some variety of formula.
But when we use undefined variable as output, can execute VIs with no errors.
We think it is a problem because when programmer makes a typo, they cannot notice the mistake.
When undefined variable is used as output variable, LabVIEW should forbid to run VI.

I think you are going to get the same (or similar) answers than to my suggestion(s) to make VI outputs potentially "required" and the same for some functions (built-in VIs):
http://forums.ni.com/t5/LabVIEW-Idea-Exchange/Allow-required-outputs-in-VIs/idc-p/3157058
http://forums.ni.com/t5/LabVIEW-Idea-Exchange/quot-Function-terminal-not-connected-quot-detection-plus/idi-p/1858573
In general, I agree with you, there is a potential for problems. Not really for the reason you are mentioning, because a typo will break the VI (unless you have two output variables with very similar names - unlike in your example - such as y and y0). But it could make for some frustrating debugging session.

Formula Node Floor(x) Produces Different Result

Hi, A search didn't find anything about the Floor(x) function, so... I'm using LabVIEW 6.0.2, and the Floor(x)function in a Formula Node seems to be producing different results depending on previous calculations. I've got the following 2 lines in a Formula Node:
MSS = Ref / RefDiv;
MDN = floor(RF / MSS);
Ref is always 20.0M, RefDiv always 500.0, and for this calcualtion RF is always 1539.4, all numbers Double with 6 digits of precision. I generate an array of frequencies given a start, step, and frequency count. These frequencies then go to a subVI with a Formula Node that calculates the byte values to send to a couple PLLs.
If Start = 70.1, Step = .025, and Count = 20, at frequency 70.2 the Floor function gives 38.485.
If Start = 70.0, Step = .025, and Count = 20, at frequency 70.2 the Floor function gives 38.484.
I've omitted some calc steps here, but I've verified the starting values in the subVI are the same in both cases. Why the result changes I'm hoping someone can tell me...
Thanks,
Steve

I want to thank those involved again for their help. With ideas and hints from others I found a solution without scaling.
In recap, what had bothered me was it *appeared* like the same subVI was giving correct results one time and incorrect results only randomly. While I understand binary fractional imprecision, I wasn't doing any looped calculations 100+ times or anything.
I did some more checking though. The problem was indeed introduced by cumulative fractional addition. In this case 10 additions were enought to cause the error. Apparently, floor(71.199_94) produces 72.0. However, using a shift register and constant fraction to add an offset to produce an array introduces enough error in under 10 iterations to be a problem. By the time the loop got to what was supposed to be 72.0, it was actually 71.199_84 or something, enough to throw the floor function. Now I understand why the error occurred, and why it wasn't a problem before.
I fixed this problem by changing the real frequency number to a I32 before introduction to the formula node. This corrected the error introduced by the fractional addition by forcing 71.199_84 to 72, instead of letting it propagate through the rest of the calculations. And it was a whole lot easier than changing all the VIs to allow scaling! Also, I prefer to know where and why the problem happened, instead of just scaling all my calcualtions. Maybe I can recoginse potential problems in the future.
My boss wants to go back and look at his program to see if HPVee somehow bypassed the problem or if he did the calculations differently.
Thanks again for the insight and help,
Steve

Why do I receive Error -23088 when using the Eval Formula Node.vi (LV6.1)?

Hi,
I want to evaluate formulas like x=v>20; with that vi. When typing the
same formula into an normal Formula Node I get the correct answer. When
changing the formula into x=v+20; the eval Formula node.vi works fine.
But whenever I try to resolve a boolean function like that mentioned
above, I receive that f****n Error! Why this? What can I do? Is the Eval
... .vi less powerfull than the normal node?
Thanks for your help,
Daniel

Joel A wrote:
> I think the boolean (binary) ops are the only difference between the two nodes.  I pulled this from the help:
> Formula Node and Expression Node Functions
>
> The following list contains the names of the Formula Node and Expression Node functions, and their descriptions. Except for the binary functions, you also can use these functions with <a href="gmath.chm::/Parser_VIs.html" target="_blank">Formula VIs</a>. All function names must be lowercase. You also can use <a href="mk:@MSITStore:C:\Program%20Files\National%20Instruments\LabVIEW%208.0\help\lvhowto.chm::/Precedence_of_Operators_in.html" target="_blank">operators</a> and the pi constant in Formula and Expression Nodes.
> Start at the help above, and see if you can find any helpful information.
>  
>  
> J
Thanks for help,
I solved the problem by using the "Parse Arithmetic Expression.llb" from
examples. You can modify it and add the operators you need..

Formula node related VIs

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