#intersection of a step function and a ln based function

70 messages · Page 1 of 1 (latest)

dull marlin
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@tacit yarrow

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look

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composite step function and log

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8 intercepts

tacit yarrow
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oh wow i have underestimated its complexity

dull marlin
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you can give it a shot

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@tacit yarrow =ln(X+3)

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couldn't fit it all on screen

tacit yarrow
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latex

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use the texit bot

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also hell nah brother

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no way in hell im solving it

dull marlin
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also using approximations of the sum function can exponentiate the number of intercepts

tacit yarrow
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how can you find the points where this function abruptly changes direction

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like, all these spikes

dull marlin
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this is one of the spikes with an accuracy of n→30

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30 is one of the approximation points that doubles the number of intercepts

tacit yarrow
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whats the second derivative at this point

dull marlin
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you done derivatives with sums?

tacit yarrow
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dont you just differentiate each term in the series and find the sum?

dull marlin
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the derivative of a sum is the sum of the derivatives yes

tacit yarrow
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brother im only finishing calc 2

dull marlin
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so you have a progression of derivatives

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it's a real fun time

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I'll brb after taking the 2nd derivative of the sum

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-4nsin(2nx)/π

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not bad

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nvm it's worse

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desmos took a while

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the peaks are infinite at n→∞ as expected

dull marlin
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then you just apply that to the 1/6x slope

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bottom points lies on y=1/6x, top on y=1/6x+1

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then you can redefine your bases if you want

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so it remains π/8+nπ

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or you can do trig to find those points

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(π/8+nπ)(6/√37)

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cos(arctan(1/6))→cos(arccos(6/(√(1+6²)))=6/√37

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so now you have a nifty new formula for contact points with each of the lines

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oh yeah peaks are 7π/8+nπ

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then you can do recursion to find xs

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@tacit yarrow so you see, not Bad (I would end my life if I actually had to do this)

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proposal for a server challenge:
form a general formula for the intercepts of a step function with an arbitrary slope and a log based function, with workings, in the simplest possible way

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I've realised that the 1/6x 'rotation' is actually a rotation and squish

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yeah seems like a waste of time

dull marlin
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straight lines

tacit yarrow
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keke

dull marlin
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oh I've had an idea for the step function thing

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yeah it would make it a whole lot easier

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it's very beautiful

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doesn't fit in this margin

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only thing left is me dying and some bloke discovering it 400 years later

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did I ever have a strategy? who knows

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anyways my actual idea was to define it as a piecewise function, then you can solve for the points geometrically

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seeing as that piecewise function is what the Fourier transform is tending to

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why not skip to the chase and just work with the piecewise function

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also works much better under the rotation that I'm actually trying to apply

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rather than needing scaling on the X component

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still needs W but a lot simpler

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I should sleep more often, maybe then it wouldn't take me 30 minutes of waffle to come up with an obvious solution

verbal tartan
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U need to be sure that the series is unif convergent

dull marlin
dull marlin
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I was taking the derivative of an approximation

verbal tartan