Standard x(t) integration vi: could be improved

Question

Problem with standard Labview Integral x(t).vi (time domain)
What it does:
Performs the discrete integration of the sampled signal X. If Y
represents the output sequence, Integral X; the elements of Y are
obtained using the following equation:
Y[i] = Y[i-1] + (1/6) (X[i-1] + 4*X[i] + X[i+1]) dt.
for i = 0, 1, 2, ...n-1.
where n is the number of elements in X.
Y[-1] = 0.0 (AArgh!)
X[-1] is the initial condition
X[n] is the final condition
The fact that Y[-1] is systematically zero prevents this vi from being
used for continuous buffers the way it can be with IIR filter when
setting
init/cont (init:F) to False
I guess this is a real drawback for real-time continuo
us data
acquisitions with integration.
Experience has shown that writing a dll for the standard execution
executes slower than the standard Integral x(t).vi from Labview. Does
anybody have a fast solution for integration where Y[-1] can be
initialized to the last value from the previous call to integration?
After all, X[-1] can be specified. I do not see why Y[-1] couldn't be
so.
Gérard D'Ans
Regards Meilleures salutations Met vriendelijke groeten Mit freundlichen
Grüssen
Gérard D'Ans
Laborelec: [email protected] 32 2 3820568 fax [phone]
Université Libre de Bruxelles: [email protected] 32 2 6502515
fax [phone]
URL site: http://www.ulb.ac.be/polytech/laborulb/index.htm

Answer 1

Very easy to do it by yourself:
Having a Y[-1] value different from 0.0 resutls merely of an additive
constant to the whole Y array.
Thus make a VI that calls Integral x(t).vi and remembers (in a shift
register)
the value Y[n] for the next call.
On the next call, add this value to the whole Y output array.
Have also a boolean the force reinitialisation to Y[-1] to 0.0
Jean-Pierre Drolet
Gérard D'Ans a écrit dans le message :
[email protected]..
> Problem with standard Labview Integral x(t).vi (time domain)
>
> What it does:
> Performs the discrete integration of the sampled signal X. If Y
> represents the output sequence, Integral X; the elements of Y are
> obtained using the following equation:
>
> Y[i] = Y[i-1] +
(1/6) (X[i-1] + 4*X[i] + X[i+1]) dt.
>
> for i = 0, 1, 2, ...n-1.
>
> where n is the number of elements in X.
> Y[-1] = 0.0 (AArgh!)
> X[-1] is the initial condition
> X[n] is the final condition
>
> The fact that Y[-1] is systematically zero prevents this vi from being
> used for continuous buffers the way it can be with IIR filter when
> setting
> init/cont (init:F) to False
>
> I guess this is a real drawback for real-time continuous data
> acquisitions with integration.
>
> Experience has shown that writing a dll for the standard execution
> executes slower than the standard Integral x(t).vi from Labview. Does
> anybody have a fast solution for integration where Y[-1] can be
> initialized to the last value from the previous call to integration?
> After all, X[-1] can be specified. I do not see why Y[-1] couldn't be
> so.
> Gérard D'Ans
>
>
> --
> Regards Meilleures salutations Met vriendelijke groeten Mit freundlichen
> Grüssen
> Gérard D'Ans
> Laborele
c: [email protected] 32 2 3820568 fax [phone]
> Université Libre de Bruxelles: [email protected] 32 2 6502515
> fax [phone]
> URL site: http://www.ulb.ac.be/polytech/laborulb/index.htm
>
>