[PD] RK4 for Pd

Charles Henry czhenry at gmail.com
Wed Aug 17 23:48:58 CEST 2011


Runge-Kutta is for integrating functions that you know a formula for.

So, at least in terms of signals in Pd, there's nothing better than
the simple recursion formula (x is input, y is output):
y[n] = y[n-1] + x[n]

Now, you may also want to scale by the sample rate  y=integral(0 to t, x*dt)
Then, it's just
y[n] = y[n-1] + x[n]/44100     (or whatever sample rate)

In z-transform terms we get:

Y(z) * (1 - z^-1) = X(z)
or
Y(z) = X(z) / (1 - z^-1)

which tells us we have a single real pole at z=1
So, the object I think you want is just
[rpole~ 1]

And you can apply the scaling by the samplerate as needed.

for messages, I don't know.  To integrate them over time, you would
have each value multiplied by the time in between messages.

Chuck


On Wed, Aug 17, 2011 at 4:10 PM, Jeppi Jeppi <jeppiot at hotmail.com> wrote:
> Hi all!
> I would like to know whether there is any object or abstraction available to
> perform numerical integration (at control or audio rate, whatever) for Pd.
> Any examples around there?
> Thanks in advance!
> Josep M
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