Static variable in Formula Node

Hi,
How do I declare and use a static int variable in a formula node?

Hi splee,
You can look at Formulat node Syntax
Thanks as kudos only

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How to difine global variable in Formula node?

I want to access the same vailable in different formula nodes, so I need to define a global or external vailables? How can I do this?

Formula Nodes are distinct environments from each other. You will have to define the global constant in each node. Or make it a variable and wire your values to the variable input node on each of the formula nodes.

Extended precision variable declaration in formula node?

I'm looking for a way to define my variables inside my formula node as extended precision but everytime I attempt this, I get an error. To my understanding, the declaration should be "long double" but it does not seem to work. Anyone have any ideas?
Greycat

Thanks Dennis ... I guess sometimes it seems quicker to ask instead of looking... but then I found what you were referencing very quickly. Just being lazy I suppose!!! Anyway, thanks for the help.
Greycat

I need in Formula Node to assign to the variable value 4000000000!!! What kind of variable it should be???

i've just tryed to write unsigned in32, but it does not understand 'unsogned'... But i need variable to be unsigned, because the max value = 4000000000... So, how can i solve this probleme???

Hi,
I don't see exactly what you're trying to do here.
Where do you want to assign the variable 4000000000 to? If you want it as an
input, just use a dbl, with only zeros behind the coma.
Note that an integer is a number without any decimals. An integer in LabVIEW
is this, but with an extra limitation that it can only be 32 bits... So a
dbl can be an integer.
If the input dbl is not an integer, use round, round to -inf or round to
+inf to make it one. This can also be done if the output needs to be an
integer.Inside the formula node floor(x), int(x), intrz(x) or ceil(x) can be
used to make integers.
I hope this is what you mean... I can't see any problems doing this.
Regards,
Wiebe.
"DrON" wrote in message
news:506500000008000000E
[email protected]..
> I need in Formula Node to assign to the variable value 4000000000!!!
> What kind of variable it should be???
>
> i've just tryed to write unsigned in32, but it does not understand
> 'unsogned'... But i need variable to be unsigned, because the max
> value = 4000000000... So, how can i solve this probleme???

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 with global variable

Hi,
I am tring to use formula node with global variables as an input and output,
but this is where I see the SW hangs forever.
By the way I am a novice to the labview.
Can some give me hint why this is happening?
Thank you in advance,
Do
Solved!
Go to Solution.
Attachments:
formula_node_wGlobalInputOutput.JPG ‏281 KB

Well, the first case of the two loops has a direct LabVIEW translation like this:
However, just because that's the direct translation doesn't mean that's what you should be doing. In the formula node it seems as if you were copying elements from one array to another. Element-wise operation on arrays via loops can be quite inefficient in LabVIEW. Often one can operate in place with arrays, and an operation that would require two loops in a language like C would actually require no loops in LabVIEW. In fact, with the above example, even if you were to use loops, arrays can auto-index for-loops so you don't even need to wire the constants to the N terminals to tell the loop(s) how many times to run.
Can you describe what you're trying to accomplish? There's likely to be a more natural way to do it in LabVIEW that would require no loops. Have you gone through the tutorials? You can also look over the material in the NI Developer Zone's Learning Center which provides links to other materials and other tutorials. You can also take the online courses for free.

Formula node does not accept complex variables

Is there any way to make formula node accept complex variables. I do not talk about dividing it to Real and Imag, but to have genuaine complex as an input.
thanks in advance
Pawel

Available data types are given in the following document:
http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/d6bed7d73659c43586256a7300691c26?OpenDocument
MTO

Formula node output variable

I have a formula node with an output variable. When i run my program the first time the output is correct. But when i run it after that, only the previous output value is displayed, the variable is not refreshing. It seems as if the value is copied into the memory and is not being updated. Is there a property for the output variable that must be changed?

The formula node should update the output each time it is run. There is no property node for the ouputs.
Ensure that (1) your inputs are actually changing as you expect - use a probe to confirm and (2) that the indicator you are looking at is wired to the output correctly.
Post an example of the problem you're seeing if you still have a problem
Tim

Formula Node variable assignment problems

I have a formula node with the follwing:
Inputs:E,X,T,PD,I
OutputsK,PD
The statement inside the formula node is:
if (Eelse if (PD=1) if (E else if (E<=X) ;
else PK=I, PD=1;
The logic seems to be working the way I want, the problem is in the last else statement. PK is never assigned the value of I. however, PD is assigned the value of 1. There are no errors indicated.
The source of the I input is the iteration # of the For loop where this formula node is located.
Anyone see what I am missing??
Thanks,
Mike

Mike,
In comparisons, == should be used instead of =. This is a very common mistake, and a reason that forumla nodes should be avoided if possible (except of course for very long formulae that would require a lot of nodes.
It looks like your code would be better represented with LabVIEW nodes instead of in a formula node (for readability - there is no performance difference.)
Also, you may wish to reconsider using an Input variable that has the same name as an output variable. Try using PDi and PDo, or PD1 and PD2 instead.
Good luck.

Formula node uotput variable

If i use two different formula nodes with the same output and input variable names will the variables (scope) be the same? In the first formula node i define a variabe "int32 first ==0" then in a seperate node embedded in a for loop structure I write " if(first==0) first = chan;". That way the variable "first" is set equal to "chan" only once through all acquisitions of the for loop b/c "first " only equals 0 at the beginning of the loop. My problem is that after running the program more then once the value of "first" remains the same regardless of the new value of "chan".

I believe that the variables are local to the formula nodes themselves.
Therefore, in your first formula node, first is set to 0. In the second, if you don't define an initial value, it is assumed zero. So the first time through, it will get set to the value of chan. But the second time through, it already equals chan in the second formula node (not reset by the first formula node--they are separate variables). Therefore, it will never go to a new value of chan until it is reset to 0.
Mark

Eval Formula Node variable names

I am using the Evaluate Formula node to allow programatic changes to formula
in my data acquisiiton VI. Has anyone built any code to enable using full
descriptive names as variables, instead of the a0 to z9 that this VI limits
you to?

You can replace full decriptive names with short names like a0...z9 using Substitute Variables.vi, which you will find at 'Mathmatics'->'Formula'->'Advanced Formula Analysis'.

Array output from formula node with input variable as array size

Hi,
I have created a formula node with an array output called al, but I get an error "you have connected a scalar type to an array with that type".
I declare the output as follows..
float64 al[len_as];
where len_as is an scalar input to the formula node.
It only works when I put a number as.
float64 al[5];
,but I don't know beforehand how many elements I need, so I cannot use this.
Please help! This is so stupid.
Thanks

Don't define your array in your formula node.
Initialize the array as the size you want and pass it in as an input into the formula node.
Are you sure you even need to use a formula node? Can you implement your formula using all native LabVIEW functions?
Message Edited by Ravens Fan on 10-07-2009 11:51 PM
Attachments:
Example_VI_BD.png ‏3 KB

How a can restar all my variables of some "Formula nodes"?

I have one formula node with several outputs,
I want restar one of her value to 0 when one sentence is false o is true.

I am not quite sure what you are wanting to know. I suspect that you want to be able to write if-then statements (conditional ) in the formula node. The best place for this kind of information is to right click on the boarder of the formual node >> help.
I dug around for a few seconds and found the following cryptic information:
The numeric value of TRUE is 1, and FALSE is 0 for output. The logical value of 0 is FALSE, and any non-zero number is TRUE. The logical value of the conditional expression
is if the logical value of is TRUE and otherwise.
I think this means if is true then do otherwise do
There is an example that might be more helpful. Open LabVIEW >>
help >> find examples >> click on search tab >> look for formula >> open calculate volume.vi .

"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 .

Formula node uInt32 overflow

I'm having a weird behaviour in formula node. The overflow of unsigned integer operations simply doesn't match the results of standard LabVIEW blocks as shown in the attached picture.
How can I deal with this problem? I need the behaviour of the block diagram. I could not do a right logical shift in unsigned integers in block diagram, so I'm using formula node (I could not figure out how to do it because I can't negate a unsigned value).
I'm using LV2012SP1. Were there any changes in this behaviour in newer versions?
Thank you.

I found a problem in hexadecimal and octal numeric representations of the formula node. The picture illustrates the issue. Three variables are assigned with the same value but outputs different results.
The hex and octal representations only work for half range of the 32 bits unsigned integer. When the value assigned gets beyond this limit the variable receives zero. This doesn't happen with a decimal value neither with 8 bits variables. Seems the problem doesn't only happen with overflow operations.

Static variable in Formula Node

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