Matlab to Labview

[AR_1000]

Dear All,

I have the following MATLAB code. I tried it in mathscript node in Labview 8.6, but the execution was slow.

How can this be converted into Labview.

X: array that contains max values

S: orginal signal

for i= 1 : (length(X)-1)

if (X(i+1)-X(i)<50)

        m(k)=S(X(i));

        k=k+1;

else

        m(k)=S(X(i));

        [mx,ind]= max(m(1:k));

        max_val(n)= mx;

        max_ind(n)=X(ind);

        m=0;

        k=k+1;

        n=n+1;

end

end

Thanks

Your help is much appreciated.

[Pachi]

Hi,

I can either tell you how to do it, or teach you. What would you prefer?

Regards,

Prashanth

[AR_1000]

Hi Pachi,

Of course I prefer to teach me. Alot of my coding depends on getting to know how to do it.

Regards,

[altenbach]

Why don't you attach your matlab code and include some typical data.

Why is "m(k)=S(X(i));" in both cases. Wouldn't it be sufficient to have it once before the decision then?

[AR_1000]

Dear altenbach,

The two statements should be there to include the last point of X since the for loop i=1:length(X) - 1

Look at the attached sample data and m file.

Regards,

[Pachi]

AR_1000,

Are you comfortable using lor loops and case structures in LabVIEW?

If not, here are some useful links:

https://decibel.ni.com/content/docs/DOC-15757

http://zone.ni.com/reference/en-XX/help/371361H-01/glang/case_structure/

https://decibel.ni.com/content/docs/DOC-17034

Your code needs a very simple understanding of how loops and case structures work, and the basics of input/output (controls/indicators)

Regards,

[AR_1000]

Tanks Pachi for the links.

I think I know how to use loops and cases .

The main problem how to handle arrays and their elements inside looping structures as described in the matlab code above.

[Pachi]

Yes, for that you will need to know the concept of auto-indexing in loops.

LabVIEW allows you to automatically access each element of an array in an iteration by auto-indexing.

For your application, use a array control or constant autoindexed to a for loop (note that you no longer have to tell the loop what the value of N is)

[AR_1000]

Please at the VI attached. It is a simple try to implement what I understand so far. But I could not complete it.

Any suggestions?

[Pachi]

Hi,

This is exactly why I asked you to study auto-indexing and shift registers, These concepts inside loops greatly ease your programming in LabVIEW. 

Here's a quick introduction to them:

When you wire a signal into and out of a loop, you can either have a tunnel, auto-indexed tunnel, or a shift register.

A tunnel takes a copy of the value and uses this for each loop iteration.

An unto-indexed tunnel indexes out elements of an array for each iteration

A shift register is a feedback loop and sends the output of an interation to the next.

For your application, your S needs to be a tunnel and X needs to be auto-indexed. Right click the tunnel (orange box on the loop) on the X signal and click "Enable Indexing". Notice that you no longer need to wire the N-input of the for loop. It understands that the loop should run for each element of X.

Regards