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 .

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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)

PV cell equation error in formula node

Hi! I am currently building a PV system simulation in LabVIEW with maximum power point tracking, and I'm trying to make this VI work using the formula node but I can't run it due to an "array indexing problem". The VI is based on the LabVIEW's toolkit for IV characterization using the equation for the PV cell current. I added the XY graph to graph the current and voltage from the equation. I'm really new to LabVIEW, so any suggestion will be greatly appreciated. I have attached the VI I'm building.
Solved!
Go to Solution.
Attachments:
eqn_based.vi ‏11 KB

Hi spectre,
the formula not cannot calc with arrays the way LabVIEW does:
(Check for correct computation against given formula...)
Best regards,
GerdW
CLAD, using 2009SP1 + LV2011SP1 + LV2014SP1 on WinXP+Win7+cRIO
Kudos are welcome

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...
Brian

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

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)
A1=V;
Thanks,
Philip

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>
<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.

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.

Formula Node Troubles

I'm a beginner with LabVIEW and I am working with the formula node. My program is not running. The error I am recieving is "array indexing expected". What exactly does that mean? All my input arrays are defined outside of the node.

a1wd3 wrote:
I'm a beginner with LabVIEW and I am working with the formula node. My program is not running. The error I am recieving is "array indexing expected". What exactly does that mean? All my input arrays are defined outside of the node.
You need to index your arrays in the formulas. Are you trying to get arrays going out? Scalers and arrays do not mix inside of the formula node. You could probably do all of that in actualy LabVIEW code instead of using the Formula Node.
There are only two ways to tell somebody thanks: Kudos and Marked Solutions
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LV 6i: Serious Formula Node problem!

I have found a "serious" problem converting VI from LV 5.1.1 to 6i:
I have same "big" equations for density calculation with upper 65 coefficients
and 3 o more inputs variables.
Everything goes well and fast in 5.1.1, when I open this VI in LV 6i there
is automatically conversion
of exponential symbol (from "^" to "**") with non apparent problem,
but the result of equation is WRONG, very, very incorrect (from 0 in 5.1.1
to same negative milliard...).
I tried with more different equations and the results are similar...
For the last: when I re-convert my VI in version 5 and run it in LV 5.1.1
everything re-work PERFECTLY! Strange.
Have I found a "terrible" BUG?
Someone have found the same problem?
Do you have some ide
a?
I will wait some news from you.:-)
Thanks for reading this LONG news.
Bye, bye.
Alfio.

"Alfio" wrote:
>>I have found a "serious" problem converting VI from LV 5.1.1 to 6iI have
same "big" equations for density calculation with upper 65 coefficients>and
3 o more inputs variables.>Everything goes well and fast in 5.1.1, when I
open this VI in LV 6i there>is automatically conversion>of exponential symbol
(from "^" to "**") with non apparent problem,>but the result of equation
is WRONG, very, very incorrect (from 0 in 5.1.1>to same negative milliard...).>I
tried with more different equations and the results are similar...>For the
last: when I re-convert my VI in version 5 and run it in LV 5.1.1>everything
re-work PERFECTLY! Strange.>Have I found a "terrible" BUG?>Someone have found
the same problem?>Do you have some idea?
>I will wait some news from you.:-)>Thanks
for reading this LONG news. >Bye, bye.>Alfio.
Hi Alfio
Some times ago I had a simmilar problem but with labview 4.x. My equation
in the
formula node was (and still is) very large too but the problem was related
with the
x^2 terms. When these terms were changed with x*x the vi worked fine. Very
strange.....Also, this problem did not appear with small equations. Try a
smaller equation and see what happens. And more: with LV 5.1 (I am using
this version)
there is no problem.
Good luck.
Ricardo.

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?
I'm confused as to why I can build and run the program on my machine. I have LabVIEW 7.0 and Windows XP. What version of Windows and LabVIEW are you using? Also, are you getting the error window when you try to build an executable or when you attempt to run the VIs within LabVIEW?
Regards,
-Joe-
Attachments:
tutor.JPG ‏100 KB
tutor2.JPG ‏122 KB
detector.JPG ‏46 KB

Labview 8 with application with MatScript node hangs

Hi,
I have a application build with Labview 7 adapted with Labview 8, more specifivaly I included a MathScript node. It works just fine in the development environment. But the compiled exe hangs when it starts with code in the Mathscript node.
Anyone an idea?
I used the MathScript node because it was a convenient way to implement a filter, but the time saved with the implementation is now lost due to the exe problems.
I have a vi attached with the actual Matscript node (without the rest of the program). This vi has also the same behaviour: working in the development environment but not stopping to run when I have build an exe.
Anyone an idea how to solve this problem?
Attachments:
CDM_filter_P_mat_TESTVI2.vi ‏356 KB

Hello,
The Application Builder in LabVIEW currently does not support building VIs into EXEs that contain a MathScript node. R&D is already aware of this problem (issue #3OGC1FLN), and we will be looking to fix the problem in a future LabVIEW version. To my knowledge, your only possible workarounds are to write the code in LabVIEW (I'm no MathScript expert, but it doesn't look like it would be too difficult to translate this script into standard LabVIEW code), or to use a Formula Node (I'm also not sure if the Formula Node would support all the operations you're doing in the MathScript node).
Good luck,
-D
Darren Nattinger, CLA
LabVIEW Artisan and Nugget Penman

Labview. Writing an equation inside a formula node

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