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

Similar Messages

  • 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

  • Formula node output on the right hand side

    I want to use formula node to find the  independent variable (right hans side equation). For simiplicty let us say y=x+z. When I make z as the output it gave wrong answer but when the y is output, it works fine. I have a more complicated equation which prevent modification to make the output on the left hand side. I attached the VI

    Husain111 wrote:
    I want to use formula node to find the  independent variable (right hans side equation). For simiplicty let us say y=x+z. When I make z as the output it gave wrong answer but when the y is output, it works fine. I have a more complicated equation which prevent modification to make the output on the left hand side. I attached the VI
    LabVIEW does not contain a symbolic math solver. If you cannot rewrite the formula in the way you want (try wolfram alpha!), I would probably use newton-raphson to find the solution. It ypically converges very fast. Make sure there is only one unique solution and that you know a reasonable guess.

  • Changing Output type in Formula Node?

    I looked at some other posts on how to set a formula node output as an array, and am unsure why it is not an array. Here is the text in my node: ("out", "in1", and "in2" are all supposed to be 2D arrays; i is an int)
    int32 out [50][50];
    if (i==0)
    out = in1;
    else
    out = in2;

    Hi,
    you must use something like
    int32 out[50][50];
    int32 j, k;
    if (i==0)
    for (j=0; j<50; j++)
    for(k=0; k<50; k++)
    out[j][k]=in1[j][k];
    else
    for (j=0; j<50; j++)
    for(k=0; k<50; k++)
    out[j][k]=in2[j][k];
    I think this is because formula node must be precompiled before execution of your VI. In your case it doesn't know how to address different array elements of "in1" and "in2" because it doesn't know its sizes before you start your VI. In my example I specify the adresses of array elements by using indecies [j][k].
    In any case it looks like you can't make direct assignment of arrays like "arr1=arr2". You always must assign its elements in a loop like "arr1[i]=arr2[i]".
    Good luck.
    Oleg Chutko.

  • 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

  • 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

  • How to program a C like pragraming in formula node?

    I need to write a simple C like progarm in the the formula. The below is the program.
    int x, i ;
    float large;
    large=a[0];
    for(i=1; i<202; i++)
    if(a[i]>=large)
    x=i;
    return x;
    But Labview thinks there is an error in it. But I can not find the error.So, anyone can help me?

    If you use a Formula Node, you need to do something like this.
    int x, i ;
    float large, large707;
    large=a[0];
    for(i=1; i<202; i++)
    if(a[i]>=large)
    large = a[i];
    x=i;
    large707 = large * 0.707;
    Then you need to add Formula Node outputs for large and large707.
    Note that I added the line large = a[i]; to save the new max to large.
    If you use Array Max & Min, use the Multiply function from the numeric palette to multiply the max value by 0.707. Look at the LabView help for Array Max & Min.
    Look at the attached example.
    Attachments:
    ArrayMax707.vi ‏26 KB

  • 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

  • "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 .

  • In formula node how to use array outputs

    someone has talked about this. but it is still a problem to me.
    no matter how i declare the variable, the output terminal keeps a scalar.

    You should be able to declare it using:
    int32 VarName[x][y];
    That should make an array of 32bit integers.
    See one of my earlier posts here: http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RPAGEID=135&HOID=506500000008000000EE2C0000&UCATEGORY_0=_49_%24_6_&UCATEGORY_S=0&USEARCHCONTEXT_TIER_0=0&USEARCHCONTEXT_TIER_S=0&USEARCHCONTEXT_QUESTION_0=array+formula+node&USEARCHCONTEXT_QUESTION_S=0
    Try copying the code that I posted into your formula node and see if you get an array out. Or try the example I attached with the same code in it.
    Let us know if you are still having trouble.
    Brian
    Attachments:
    ArrayFormulaNode.vi ‏23 KB

  • 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 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.

  • Can formula node take string input and output string?

    I am wondering if the formula node can take string input variable and output string variable after calculation. otherwise I have to output integers and then use case structure to select different output strings, that is kind of redundant in coding.
    ping

    If you are just trying to read lines that have mixed formatting, you don't need any script nodes.
    Can you attach a tpyical flne and a description of the desired read operation so we have a better idea what you are trying to do? Do all lines have the same overall format?
    LabVIEW Champion . Do more with less code and in less time .

Maybe you are looking for