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Re: How to calculate the abscissa values for the given vertical values [message #68131 is a reply to message #68130] Mon, 05 October 2009 06:43 Go to previous message
duxiyu@gmail.com is currently offline  duxiyu@gmail.com
Messages: 88
Registered: March 2007
Member
Maybe my statement is not clear.

There is a function Y=F(X), and I want to calculate the correspondent
abscissa values X for Y=0.
It means that there are serval intersection points between the line Y=F
(X) and the horizonal line Y=0,
and I want to get the correspondent abscissa values of these points.


On Oct 5, 3:10 pm, Wox <s...@nomail.com> wrote:
> On Mon, 5 Oct 2009 01:56:20 -0700 (PDT), "dux...@gmail.com"
>
> <dux...@gmail.com> wrote:
>> Hi, all.
>> I want to calculate the abscissa values for the given vertical values.
>
>> For example,
>>     x = findgen(1000)/1000*4*pi
>>     y = cos(x)
>> I want to get the abscissa values for y=0.
>> For this example, the results shoule be [!pi/2, 3*!pi/2, 5*!pi/2, 7*!
>> pi/2].
>> But how can I get it by IDL codes?
>
>> Best wishes,
>> jdu
>
> Just for this function:
> print,(indgen(ceil(max(x)/!pi))+1)*!pi/2
>
> What do you need exactly? You can always find the answer analytically
> no?

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