How do I enter this formula

[asmit172]

Hi,

I am new to labview and I have managed to set up a VI that tracks and records center of pressure (COP) using a force plate. I have a couple formulas that I need to enter into this VI to calculate specific measures of balance. The problem is I don't know how to enter them. An example of an equation is:

Path length

P=f/(N-1) ∑_(I=1)^(N-1)√([x_I+1- x_I]^2+ [y_I+1-y_I]^2 )  

f = the sampling rate (sampling at 1000Hz)
N = the number of samples 
x_I = the instantaneous COP in the mediolateral direction at sample index I
y_I = the instantaneous COP in the anterior-posterior posterior direction at sample index I

The VI I have set up acquires x and y. Do I require the Mathscript Node to enter this equation or how should I go about it?

[altenbach]

Do you have the formula in graphical form. It is a bit hard to read as a plain, single-line text. What is the format? What is the meaning of the underscore? The caret?

[Mark_Yedinak]

Take a look at the formula node. You should be able to do what you want using it.

[Mark_Yedinak]

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@altenbach wrote:

Do you have the formula in graphical form. It is a bit hard to read as a plain, single-line text. What is the format? What is the meaning of the underscore? The caret?

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I believe the underscores are there for readability to separate variable names and that it implies multiplication. x_I would translate to X times I. X^2 would be X squared.

Of course the original poster should verify my assumptions.

[altenbach]

Try this:

[asmit172]

I have attached the formula as a word document for clarification.

[altenbach]

My example abouve will do exactly that.

For the x and y array, we clip the first element, then subtract the full array. We get an array with one less element containing (x(i+1)-x(i)) or similar.

Forming the complex array and taking the absolute value is the same as taking the square root of the sum of squares for each element.

Taking the mean is equivalent of summing, then dividing by the (new) size (n-1).

(If you don't like complex, you can do it more explicit, it'll just be a little bit messier ;))

Multiply by f to get the result p.