how can i change Y-axis into log and dont get Warning: Negative data ignored

I am writing a Programm that turned both Axis into log10, here is my Programm:

x=real(lambda)/W0;

y=imag(lambda)/W0;

figure

plot(x,y,'*')

set(gca,'xscale','log')

set(gca,'yscale','log')

grid on

Lambda and W0 are two Input Data.

This Programm run very well when i just delete 'set(gca,'yscale','log')', but with this sentence then a Warning Negative data ignored will be pupped out. Is there any way that will let my y-axis being turned into 'log' and at the same time with negative data?

PS: i also tried LOGLOGPN but my plot is a lots of dots not a line so its also not working.

Mit freundlichen Grüßen

Ting Zhu

[zhu ting]

and here is what my data for example:

lambda=[-1;-2;-3+2j;-3-2j;-4+3j;-4-3j];
W0=1;

Answer 1

[Kirby Fears]

Hi Zhu,

The log function is undefined for negative values. Have a look at the wiki page .

Matlab can't apply log to the negative values, so it just ignores them.

Hope this helps.

[zhu ting]

but all my X-data are negative values and ist working without any Warning. Do u know why?

Here is my Input for example:

lambda=[-1;-2;-3+2j;-3-2j;-4+3j;-4-3j];

W0=1

Thanks

[Kirby Fears]

Log is not applied to the X values. Look at the X axis before and after the statement

 set(gca,'xscale','log')

You will see that the X axis still has the exact same values as before. The values are only repositioned along the axis.

This allows you to plot log(y) against the original x values that generated y, but spaced in such a way that the plot is more readable.

Hope this helps.