Re: matrix difference

Hi Olivier,

>> I woulk like to visualize the difference of two matrices in log scale.
>> ... problem ... negative entries, ...

This seemed more complicated to me than patching the code of THistPainter. So I made a crude hack to get more or less what I want. The patch is in the attachment. It adds a new "suboption" nphh (negative-positive-half-half) to col(z) which maps, also in logscale where z'=sign(z)*log(abs(z)) for |z|>1 and z'=0 otherwise, all negative z(') to the first half of the palette, and all positive z(') to the second half, each half with its own scale. Also a little macro setting a color palette for red=negative and blue=positive is attached. The TPaletteAxis class is not adapted, so colz shows a completely wrong color scale.

A+

Alexander