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From: Samuel Fogarty
Subject: Re: Exponential Data
Date: Fri, 7 Mar 2008 11:02:13 +0900
Newsgroup: public.teechart5.cppbuilder  

Hi Narcis,

Thanks for the information.

I appreciate that log(-x) is invalid, but, I think you can appreciate the
imporatance of reasonable scaling on exponentially varying values that vary
around 0. I can't just discard half my data set. What we are talking about
is negative logarithmic *scaling*, rather than negative logrithmic
*values* - which is a perfectly valid and functional thing to do. Logically
speaking, I'm not taking the log of these values, I am simply scaling them
graphically to make them more visually useful on a logarithmic axis that
varies from positive to negative(plotting them linearly is severly limiting
for this type of data).
Plotting the data on a negative x axis is not plausible in this case,
because the viewer needs to see a line that varies above and below our
horizontal zero.

I believe it is as simple as doing "if(y < 0) y = -log(abs(y))" for me to
convert my own data to the scale it would be if I wanted it as psuedo
negative log(in this state I could plot it on a negative linear scale and
the user wouldn't know the difference, assuming the axis tags were right).
So, is there an easy way for me to have my own axis tags where I want them?



"Narcís Calvet" wrote in message
news:yBP%2386seIHA.3036@TEEPC.Steema.local...
> Hi Samuel,
>
> For log axis all values have to be positive (>0). log(-x) simply doesn't
> exist so I think there is no point in plotting them in log scale. I'd
> filter out negative values and plot only positive values.
>
> Or alternatively, plot positive values as log(x), x and negative values as
> log(-x),-x.
>
>
> Regarding log to linear scaling I can only think of using 2 series for
> that, one for logarithmic values and the other for linear values. Then use
> custom vertical and horizontal axes to display desired scales and position
> each series where desired.
>
> --
> Best Regards,
>
> Narcís Calvet
> Steema Support Central
> http://support.steema.com
>
> "Important note: If you are a TeeChart registered customer, please post
> your support questions at Steema's Support monitored Forums for customers:
> http://support.steema.comom for a prompter reply."
>
>
> "Samuel Fogarty" wrote in message
> news:hN0pCUEeIHA.3016@TEEPC.Steema.local...
>> Hi All,
>>
>> I have data that varies from positive to negative values and needs to be
>> displayed logarithmically - or at least pseudo-logarithmically for the
>> negative values. Is there a way to do this? At the moment it complains
>> when I attempt it, like excell does, so are there work arounds?
>> Related to that, is it possible to have log to linear scaling on a single
>> axis - for when the data approaches zero? Or is there soem other good way
>> to do it? I'm basically trying to display data that varies exponentially
>> and may be positive or negative and even zero.
>>
>> Thanks,
>> Sam.
>>
>
>