Derivative of arrays

[efi]

Hi,

I am new to labview and this question might seem trivial to you.

Here is what I am trying to do:

I have two arrays (generated via for loops).  I want to calculate the derivative of array 1 with respect to array 2 and then plot the resulting array vs array 2.

My VI (attached) does not do what I am trying to do.

Please help.

[CoastalMaineBird]

It's hard to tell what you are trying to do.  You gave no defaults for C and C2, so I entered 20 and 30.

You threshold the B array at 70 to get a value of 6 (that means that value 70 should be at index 6 in the table, which it is).

You're then using 6 as the dT input to the derivative function.

What do you expect to see and what do you see that's wrong?

[altenbach · Accepted solution]

The dt is typically the difference between the x-values (function assumes that the x-values are equally spaced, which they are). So, to get dt, simply thake the difference between any two adjacent x-values.

All you need is a single loop, right? The formula node seem overkill, for example the division by two should be done once before the loop.

Here's how you could simplify... makes sense?

[efi]

Sorry for not being clear.  Do not pay attaention to the numbers I used, they are just for example.  The problem I have is general; I want to get the derivative of one array with respect to another one.    

In particular, I want to generate array A and B (as I did via forloop), get dA/dB and plot dA/dB vs B. 

I am guessing I might even have used a wrong function for derivative... please advise

[CoastalMaineBird]

get dA/dB and plot dA/dB vs B. 

OK, here's where you lost me. Usually you get the derivative with respect to a CONSTANT, not another signal.  dT = sampling rate is a common one.  

If what you want is truly dA / dB, then delete one element from array A, subtract the original array from the shortened array (that calculates A[1] - A[0], A[2]-A[1}, and so on: an array of delta-A).

Do the same thing for the B array. to get deltaB

Divide deltaA by delta B.

[efi]

thanks a lot. that is exactly what I was looking for...

[efi]

Thanks. This is what Christian showed nicely in the avove jpeg. file