### math is over my head

I’m trying to put an s-curve into a buffer~ to use as a lookup table,

but I can’t figure out the damn math. I gather the formula to use

would be: y= 1./ 1 + exp((b*x) -a)

b being a curve constant, & a shifting it. I was trying to peek into

a buffer using [expr 1. / 1. + exp(($f1*$f2) – $f3)] my curve

rockets up, but never levels out at the top.

Can someone who understands math tell me what I’m doing wrong?

Thank you o wise math people.

M

Couple of parentheses should clear things up:

try:

1./(1.+exp(($f1*$f2)-$f3)))

Right now you’re adding 1/1 to exp(($f1…etc., so it will never level

out. (because the exp. is going to keep growing in value.) Once you

add the parentheses, you should see the expected asymptotic behavior.

Peter McCulloch

On around Mar 6, 2006, at 4:04, mattyo said something like:

> Can someone who understands math tell me what I’m doing wrong?

Peter McC. answered your top-level question. But if you’re really

having a hard time with the math, you might want to take a look at

lp.scampf from Litter Power, which is there particularly for creating

S-shaped and other shaped-curves, doing all the hard math for you. Just

play with the number boxes in the help file until you get the shape you

want.

Here’s a snapshot showing what it looks like:

I’ve removed the alpha channel to see if that helps the folks who have

been having problems viewing Max-generated TIFFs and colors are trimmed

to 4-bit resolution to minimize bandwidth. Forum readers will probably

have to download the Litter Starter Pack (URI below) to see it; sorry,

that’s beyond my power to control.

Best, Peter C.

>

————– http://www.bek.no/~pcastine/Litter/ ————–

Peter Castine | ^

| Litter Power & Litter Bundle for Jitter

pcastine@gmx.net |

pcastine@bek.no | iCE: Sequencing, Recording, and Interface Building

4-15@kagi.com | for Max/MSP

| Extremely cool

| http://www.dspaudio.com

| http://www.dspaudio.com/software/software.html

That works!

Cheers

Roger

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