Hello everyone, I am quite new to Mathematica and have a question regarding the function Series[ ]. I have an expression called mm1a which depends on s13, which enters mm1a only as powers s13^n or roots in the form of Sqrt[1-s13^2]. Now I want to get a series expansion of mm1a and use:
Chop[Evaluate@Normal[Series[mm1a, {s13, 0, 2}]]]
I get:
0.0000522918 - 4.83811*10^-6 s13^2 - 5.33397*10^-6 s13^4
Why does it not stop at s13^2? If I use
Chop[Evaluate@Normal[Series[mm1a, {s13, 0, 0}]]]
I obtain
0.0000522918 - 4.83811*10^-6 s13^2
and the same if I try to calculate it to order "-2"
Chop[Evaluate@Normal[Series[mm1a, {s13, 0, -2}]]]
0.0000522918 - 4.83811*10^-6 s13^2
or any other order below or equal to -1. For the positive powers I always obtain two orders more than I am asking for. Now if I use first Expand and then Series, it works, but only for even powers. e.g. :
Chop[Evaluate@Normal[Series[Expand[mm1a], {s13, 0, 4}]]]
0.0000522918 - 4.83811*10^-6 s13^2 - 5.33397*10^-6 s13^4
but
Chop[Evaluate@Normal[Series[Expand[mm1a], {s13, 0, 5}]]]
0.0000522918 - 4.83811*10^-6 s13^2 - 5.33397*10^-6 s13^4 - 5.77633*10^-6 s13^6
Why is that happening? Also on my colleague's computer it is working perfectly fine for any order. We have both the full version of Mathematica, the only difference is that I use 11.3.0 on Ubuntu 16.04, while my colleague uses 11.0.0 on Windows.
