Casting inside a "formula node"

Greetings,
Is it possible to cast a U32 to a SGL - an int32 to a float32 - inside a formula node? How?
Thanks!
"Inside every large program is a small program struggling to get out." (attributed to Tony Hoare)

Re: Is there a particular reason you are attached to the formula node?
Well... we're just experimenting with the fastest way to unpack ~10,000 U32s into ~40,000 DBLs. The packed array is U32-aligned mixture of bit-mapped integers, bools, and floats - SGLs and DBLs. We've tried doing some "vector" (array) shift, mask and scale operations - which are pretty fast, but the float-unpacking seems to require a loop. After timing a For Loop structure, I wanted to push the for loop into a formula node - where I've hit a wall (without ability to cast) ...
Since the whole purpose of looking at formula node is to save time, I'm reluctant to roll my own "cast" function.
Thanks/Cheers!
"Inside every large program is a small program struggling to get out." (attributed to Tony Hoare)

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Labview. Writing an equation inside a formula node

How would I write this equation chl= (4.9467*mv) - 0.3239 inside a formula node? Thanks
Solved!
Go to Solution.

You don't even need a formula node. An expression node would suffice.
LabVIEW Champion . Do more with less code and in less time .

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).
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Can I create array inside formula node

I need to create and use array (multidimensional) inside a formula node. My LabVIEW version is 5.1.The input and output from/to formula node do not necessarily being array. Thank you.

You need to declare a variable to be an array. To declare a multidimensional array of 32 bit intergers enter this:
int32 VarName[x][y];
Where x=1st dimension size (rows) and y=2nd dimension size (columns). You can then operate on this like you would an array in a text based language. Try the entering the example below in a formula node.
int32 i;
int32 y[5][2];
for (i=0;i<5;i++)
y[i][1] = x[i]+1;
Where y is an output and x is an 1D array input.
Hope this helps...
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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:
If T1<2.0E-5 OR T1>5.5E-4 THEN GOTO 3
U7=U7+V
I have 4 items I need help with:
(1) Is 'II' the correct operator for 'OR'?
(2) Is 'goto' an acceptable operator within LabVIEW?
(3) 'U7' is building a 1D array. How do I need to define it? Is it simply 'int U7'? Also, I will add an output value named 'U7' on the formula node wall with an indicator wired to it from outside the for loop.
(4) Is my use of the equal sign appropriate or do I need to use '=='?
Thanks for the help.
Philip
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:
if (T1>=.002004 && T1<=.002584)
B1=U
A1=V;
I want to assign both B1 and A1 values when the above condition is true. I tried a comma between the U and A1 but it doesn't work as well. Should I define A1 and B1 separately? Or would this create problems?
if (T1>=.002004 && T1<=.002584)
B1=U;
if (T1>=.002004 && T1<=.002584)
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Thanks,
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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

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?
I suppose that I could add another input that is fed with the array size from the array palate but I would like to know if it can be done inside the formula node itself.

Your own advice is the only and best one.
greetings from the Netherlands

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

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>
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<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.

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???

2pi constant in formula node

How do you use the 2pi constant inside a formula node? pi(2) and 2*pi do not work. Using labview 6i.

Sorry, I forgot to attach the VI.
Attachments:
2xPI.vi ‏7 KB

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.

Using the Formula Node for PDA

I get a compile error when I use C code inside the formula node. Is it possible to use C Code inside the formula node for PDA applications? Do I have to include any file while building the executable for the PDA

Ok, I was able to successfully build an executable file without error. I attached the screen shots of your program in execution. Does this look like the desired result?
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Regards,
-Joe-
Attachments:
tutor.JPG ‏100 KB
tutor2.JPG ‏122 KB
detector.JPG ‏46 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 .

Casting inside a "formula node"

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