Chi-square

I have tried to graph the Chi-square cumulative distribution function.

My input is
f(x)=integrate((1/2)^(f/2)/gamma(f/2)*x^(f/2-1)*e^(-x/2),0,x)
where f is a ”brugerdefineret funktion…”
It works fine when f>1, but not when f=1.
I think the problem is x^(f/2-1) when f/2-1 is negative. It doesn’t help to 
change the lower limit to 0.001.

Best regards
Ib

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Re: Chi-square

Ib wrote:
> I have tried to graph the Chi-square cumulative distribution function.
> 
> My input is
> f(x)=integrate((1/2)^(f/2)/gamma(f/2)*x^(f/2-1)*e^(-x/2),0,x)
> where f is a ”brugerdefineret funktion…”
> It works fine when f>1, but not when f=1.
> I think the problem is x^(f/2-1) when f/2-1 is negative. 

Yes, you cannot raise 0 to a negative power. That would be the same as 
dividing by zero.

> It doesn’t help to 
> change the lower limit to 0.001.

It seems to work fine when I change the lower limit of integrate to 
0.001. But I don't think this makes much sense as the result will vary 
heavily depending on the lower value.

Best regards
Ivan Johansen

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Re: Chi-square

Thank you for your answer.

Ivan Johansen <graph <at> padowan.dk> writes:

> > It doesn’t help to 
> > change the lower limit to 0.001.
> 
> It seems to work fine when I change the lower limit of integrate to 
> 0.001. But I don't think this makes much sense as the result will vary 
> heavily depending on the lower value.

The result should not depend on the lower value.
I think there is a problem:
The area under the function 
f(x)=x^(-1/2)
in the intervalfrom  0.0000001 to 9 is 5.999.
But Graphs says 15.3674.

Best Regards Ib

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Q: Beta versions

Hi,
Don't know if this is simple to do, or even if it's desireable, but I think it
would be a good idea to name the insallation file for beta versions using the
Build number added to the end. Something like: "SetupGraphBetaBuild303.exe", or
similar to that.

Or are there some other means I could use to find this information out, besides
installing and reading the About box?

The file name "SetupGraphBeta.exe" is just too ambiguous as it doesn't reveal in
so many words at what version the file is.

Regards,
P. Smårs, Sweden.

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Re: Chi-square

Ib wrote:
> The result should not depend on the lower value.
> I think there is a problem:
> The area under the function 
> f(x)=x^(-1/2)
> in the intervalfrom  0.0000001 to 9 is 5.999.
> But Graphs says 15.3674.

You are right. The area from 0 to 9 is 6. Graph is using Simpson's 
formula to calculate the area, and it looks like the algorithm starts 
running crazy when you get near an asymptote. I should probably try to 
find a better algorithm.

Best regards
Ivan Johansen

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Re: Q: Beta versions

PärSmårs wrote:
> Don't know if this is simple to do, or even if it's desireable, but I think it
> would be a good idea to name the insallation file for beta versions using the
> Build number added to the end. Something like: "SetupGraphBetaBuild303.exe", or
> similar to that.

This will make it problematic to link to the file as the link changes 
when the build number changes.

> Or are there some other means I could use to find this information out, besides
> installing and reading the About box?

Currently you will have to install it to see the build number, but I am 
looking into a way to show it in the installation.

Best regards
Ivan Johansen

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Re: Q: Beta versions

On 7/12/06, Ivan Johansen <graph <at> padowan.dk> wrote:
> PärSmårs wrote:
> > Don't know if this is simple to do, or even if it's desireable, but I think it
> > would be a good idea to name the insallation file for beta versions using the
> > Build number added to the end. Something like: "SetupGraphBetaBuild303.exe", or
> > similar to that.
>
> This will make it problematic to link to the file as the link changes
> when the build number changes.

Here's an idea. You can compress the installation file into an
archive, for example SetupGraph.zip. Then the name of the archive
could remain the same but you'd be able to change the name of the file
inside the archive to reflect the build/version number.

Matt

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Re: Q: Beta versions

Matthew Low wrote:
> Here's an idea. You can compress the installation file into an
> archive, for example SetupGraph.zip. Then the name of the archive
> could remain the same but you'd be able to change the name of the file
> inside the archive to reflect the build/version number.

I could do that, but I don't see any reason why I should put an exe file 
into a zip archive.

Anyway the build number of Graph.exe is now also used in the version 
number of SetupGraphBeta.exe. You can see it in the version tab in the 
properties of the file.

Best regards
Ivan Johansen

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Number Line Graphs

Is there any way to graph solutions of single-variable inequalities on a number 
line? 

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Re: Number Line Graphs

Mary Hill wrote:
> Is there any way to graph solutions of single-variable inequalities on a number 
> line? 

Yes, you can just add a line f(x)=0, or f(x)=1 if you don't want it on 
the axis. You can use Argument range in the Insert function dialog to 
limit the line to your inequality. Endpoints can be used to show if the 
limits are included. You can set the field "The y-axis cross at x=" to 
1000 in the Edit|Axes dialog to move the y-axis out of the way.

I have attached an example that shows this.

Best regards
Ivan Johansen

;This file was created by Graph (http://www.padowan.dk)
;Do not change this file from other programs.
[Graph]
Version = 4.2
Build = 293
MinVersion = 2.5
OS = Windows 2000 5.0 Service Pack 4

[Axes]
xMin = -10
xMax = 10
xTickUnit = 2
xGridUnit = 2