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06-09-2016 07:05 AM

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Hi all,

in the description in this link http://zone.ni.com/reference/en-XX/help/370051Y-01/cvi/libref/cvierf/

it is öentioned that the erf function Erf (double x, double *erf) has 2 inputs.the second input should be an array of double but what exactly represents this inpt to the function because as far as i know erf in matlab have only one input.

Any explications please.

Solved! Go to Solution.

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**Barp** - Control, Simulation, RTT and HIL - National Instruments

06-09-2016 09:35 AM - edited 06-09-2016 09:36 AM

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You are looking in the wrong place...

This function you showed is documentation for LabWindows CVI:

http://zone.ni.com/reference/en-XX/help/370051Y-01

However, you should be looking at this document:

http://zone.ni.com/reference/en-XX/help/373123B-01/lvtextmath/msfunc_erf/

In this documentation, the function is y= erf (x), as you would expect.

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06-13-2016 02:14 AM - edited 06-13-2016 02:20 AM

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Hi Barp,

Actually, I am working in labview communications design and not labview so the "erf" function is not defined in the C node.

I searched the erf function in this link http://www.ni.com/documentation/en/labview-comms/1.0/c-ref/analysis-lib/

and it directed me to Labwindows CVI.

as you can see the error.Any other suggestions please ?

Thanks,

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** LabVIEW Champion. It all comes together in GCentral **

06-13-2016 10:09 AM

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@emnajaoua wrote:Actually, I am working in labview communications design and not labview so the "erf" function is not defined in the C node.

So why did you post this in the LabVIEW Mathscript RT forum? This discussion probably belongs over here.

You can ask the moderator to move this thread.

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06-14-2016 01:52 AM

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Hi,

I have already asked the question there but no luck so far.

also the "erf" function belongs to the mathscript RT module as I know so I wanted to search for a solution.

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**Barp** - Control, Simulation, RTT and HIL - National Instruments

Solution

Accepted by topic author emnajaoua

06-14-2016 10:15 AM

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For this product you are using (which you did not say, but looks like LabVIEW Comms , Erf function is not supported in Mathscript or as G-code.

Now you can try this code:

a1 = 0.254829592; a2 = -0.284496736; a3 = 1.421413741; a4 = -1.453152027; a5 = 1.061405429; p = 0.3275911; s = 1; if (x < 0) s = -1; end x = abs(x); t = 1.0/(1.0 + p*x); y = 1.0 - (((((a5*t + a4)*t) + a3)*t + a2)*t + a1)*t*exp(-x*x); y= s*y;

I converted from here: http://www.johndcook.com/blog/cpp_erf/

By the way, this code could also be easily integrated using C-node too.

Now, most likely Erf function will be available in future versions of LabVIEW Communications System Design.

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06-15-2016 03:57 AM

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Hi Barp,

I am sorry for not being that clear.I have tried your solution in the C node but its outputs as not correct (I don't know why by the way).So I have tried the same script in the mathscript node using this http://www.mathworks.com/matlabcentral/fileexchange/55749-error-function-stand-alone/content/erf_sta... and it seems to work.

Thanks for the solution .I missed the idea to search for a standalone function.

Best Regards,

Emna.

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**Barp** - Control, Simulation, RTT and HIL - National Instruments

06-15-2016 08:49 AM

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yes... I forgot that Mathscript requires ".*" if x is a vector. This is just natural as G-code...

Anyway, I am happy you have a solution until we have this function available for you.