comp.lang.idl-pvwave archive: archive » Re: How to calculate the abscissa values for the given vertical values

Home » Public Forums » archive » Re: How to calculate the abscissa values for the given vertical values

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: How to calculate the abscissa values for the given vertical values [message #68126 is a reply to message #68124]

Mon, 05 October 2009 09:26

Jean H.
Messages: 472
Registered: July 2006

Senior Member

duxiyu@gmail.com wrote:
> Y is a time series and X is the sampling time.
> Both X and Y are discrete.
> I don't know the analytical form of the relation bewteen X and Y.
>
> To get the vertical value NY for a given time NX, I can use 'NY =
> interpol(Y, X NX)'.
> Similarly, I want to get the correspondent time CX for a fixed
> vertical value CY.
> But the values of correspondent time are not unique. CX should be not
> a scalar but an array.
> So I cannot use 'CX = interpol(X, Y, CY)' to get these values.

You may do it by hand...

x = findgen(1000)/1000*4*pi
y = cos(x)

Ytarget = 0

;Find the 2 consecutive points that are > and < of the Y threshold value
;(don't forget to deal where a point = the value)

Xidx = where((y gt Ytarget and shift(y,1) lt Ytarget) or (y lt Ytarget
and shift(y,1) gt Ytarget), count)

then you can do a linear interpolation to find Xsolution

;y = ax+b
a = (y[xIdx] - y[xIdx+1]) / (x[xIdx] - x[xIdx+1])
b = y[xIdx]-a*x[xIdx]
Xsolution = (yTarget - b)/a

Jean

Report message to a moderator

[Message index]

		Re: How to calculate the abscissa values for the given vertical values By: Maarten[1] on Tue, 06 October 2009 04:04
		Re: How to calculate the abscissa values for the given vertical values By: duxiyu@gmail.com on Tue, 06 October 2009 00:55
		Re: How to calculate the abscissa values for the given vertical values By: pgrigis on Mon, 05 October 2009 10:55
		Re: How to calculate the abscissa values for the given vertical values By: Jean H. on Mon, 05 October 2009 09:26
		Re: How to calculate the abscissa values for the given vertical values By: duxiyu@gmail.com on Mon, 05 October 2009 08:34
		Re: How to calculate the abscissa values for the given vertical values By: pgrigis on Mon, 05 October 2009 07:55
		Re: How to calculate the abscissa values for the given vertical values By: duxiyu@gmail.com on Mon, 05 October 2009 06:43

Previous Topic:	Earn Free cash From DoEarn
Next Topic:	rois

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Sun Oct 12 16:36:39 PDT 2025

Total time taken to generate the page: 0.39610 seconds