Dead loop in formula node

Hi,
I have encountered the following problem in a formula node. Everything seems simple and right. But there is no output and the loop goes on forever. The sizes of both input arrays are the same. Need your advice. Thanks.
Rut
Attachments:
Algorithm.vi ‏11 KB

Look, I am far out on a limb here, because I am not a C programmer. Whatever you're doing would make more sense from a FORTRAN point of view.
The LabVIEW formula node uses BNF notation (check the help), which is in many ways C like. So the syntax for a FOR loop is:
for ( InitExpression ; CondExpression ; LoopExpression ) Statement
This means the loop iterates until "CondExpression" is true.
Do a google search on "C For loop" and you might find for example pages like:
http://www.hitmill.com/programming/cpp/forLoop.htm
http://www.geocities.com/learnprogramming123/Clesson8Beginner.htm
Your condExpression is "n1-1", which, during the execution of the node is a constant. For example if you array size is 50, n1-1=49, FOREVER! The condition is never true so the loop will never stop.
I hope somebody more knowledgable will chip in at one point.
LabVIEW Champion . Do more with less code and in less time .

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For loop in formula node

Hi,
I wanna do some signal processing after I got the magnitude and phase infos from FFT. But the errors say that there is undefined variables. I am just wondering that here absP and angleP are both vectors. Can I express them like what I did in the attached vi? 3x.
Huihui
Attachments:
Untitled 12.vi ‏9 KB

Hi huihui,
do you just want to know the real and imaginary values of your signal?
Why use formula node at all?
Best regards,
GerdW
CLAD, using 2009SP1 + LV2011SP1 + LV2014SP1 on WinXP+Win7+cRIO
Kudos are welcome
Attachments:
Untitled 12.vi ‏13 KB

If-then statement in formula node

**Note - The attached file shows the current block diagram.
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Attachments:
if-then_in_FN.jpg ‏18 KB

Thanks for the help. I went ahead and rewrote the program so I could omit the 'goto's. Another problem that I am having is that I want 2 statements for 1 assignment:
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Thanks,
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"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;
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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.
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(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

Hi everyone.
I have a problem with the formula node.
I want to calculate the following function:
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When I implement the formula in the appropriate box I receive a message about
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For more information I link my .VI.
Some idea how to solve this task?
Second question:
Using the formula node is faster than realize all these operations in a
different way?
I ask it because I will need to include this .VI into 5
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Attachments:
formula node.vi ‏87 KB

Hi matomato,
fastest is usually to use LabView primitives! See attachment...
Edited: made another small change to your vi: changed y0 to DBL to avoid unneccessary datatype conversions!
Message Edited by GerdW on 02-27-2008 05:11 PM
Best regards,
GerdW
CLAD, using 2009SP1 + LV2011SP1 + LV2014SP1 on WinXP+Win7+cRIO
Kudos are welcome
Attachments:
formula node1.vi ‏87 KB

How do I determine array size in a formula node

I am feeding an array into a formula node to perform an operation on. However the size of the array can be an arbitrary size. How can I determine its size to use for iterating through a for loop?
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Your own advice is the only and best one.
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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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Attachments:
shift (LV7.1).vi ‏19 KB

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Solved!
Go to Solution.

If you use the numeric primitives rather than a formula node, craziness can be avoided (well, sometimes).
Lynn

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.
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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.
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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
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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)

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];
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for (j=0; j<50; j++)
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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]".
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Hello,
I'm trying to use the formula node to subtract the previous term from the current term (or the next term minus the current term), but I can't figure out how to
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I've something along the lines of z_array[i+1]-z_array[i], but it only returns the difference of i+1-i....
Please see the attached picture.
Thank you,
Solved!
Go to Solution.
Attachments:
Formula node.JPG ‏23 KB

That would be so easy to do in pure Lv code.
LabVIEW 8.2 - 2014
"Only dead fish swim downstream" - "My life for Kudos!" - "Dumb people repeat old mistakes - smart ones create new ones."
G# - Free award winning reference based OOP for LV

Formula Node result of NaN

Hello to all,
I have done a Formula Node with the next formula:B=(2*16/3.14159*(asin(sqrt(V/Ab))-3.14159/4))-(2*16/3.14159*(asin(sqrt(Uoffset/Ab))-3.14159/4));
Ab=3.269.
V is the data entry to the formula node.
Uoffset is the mean of the 100 first values of the data that I obtain it previosly.
I know that I can not do the square of the negative number and the asin I can not do it for values greater than 1 for that reason I don´t put values greater than 3.269 into the V value never and negative values either.
I take this precautions but I obtain several times the output value of NaN I use the entry V for example:0.00061035 could be that the format of the entry it is very extends.
Also when I introduce the same data to this formula, one times I obtain some values in the out and when I execute the subVI with the same data I obtain other values in the out. Said it diferently I obtain different out for the same data in. How it is possible????
The other hand I need to do the integral and the derivate of one array, how can I do it??? And the more important how I can or what I use for the parameter dt of the derivate???
Thanks a lot
Gonzalo De Francisco Ortiz

Hi Gonzalo,
after having a first look: You have a race condition in your code: why do you use a local for the mean value instead of simple wiring?
I think that's the reason for your unexpected results!
Other small items:
- when you use auto-indexing you don't need to provide 'num of iterations' to the for-loop.
- the only difference between the 2 cases is the 'abs'-function used for negative inputs. Just do the 'abs'-function everytime and you don't need the case-structure...
- when testing numbers against zero you can use specialized functions from the comparision palette
Editing:
I attached a changed example in LV8.0
Message Edited by GerdW on 02-01-2007 01:22 PM
Best regards,
GerdW
CLAD, using 2009SP1 + LV2011SP1 + LV2014SP1 on WinXP+Win7+cRIO
Kudos are welcome
Attachments:
FormulaNode.vi ‏20 KB

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: Array Size can be specified by wiring an input ?

All
I have a formula node where I have a module which operates on an array. I want to keep the size of the array generic. So I tried keeping the array size as an input N, and initialized the array as xdim[N]. It shows an error in my formula. what am i doing wrong ?
Kudos always welcome for helpful posts

I had exactly the same issue as Spartan00.
Just for curiosity, I was comparing labview speed in initializing a gaussian array through both the normal graphic code and the formula node.
The formula node proved to be MUCH, MUCH faster.
float m = 0.5, s=0.5, x;
int i;
float y[1000000];
for(i=0; i<1000000; i++) {
x=i*1e-6;
y[i]=exp(-pow((x-m),2)/(2*s));
Unfortunately, I can't wire the array size as an input.
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Has anybody ever tried to do the same?

Dead loop in formula node

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