# Example $$SL(2,R)$$¶

Recall the $$K\backslash G/B$$ elements of $$SL(2,R)$$:

atlas> set G=SL(2,R)
Variable G: RealForm
atlas> G
Value: connected split real group with Lie algebra 'sl(2,R)'
atlas>
atlas> print_KGB (G)
kgbsize: 3
0:  0  [n]   1    2  (0)#0 e
1:  0  [n]   0    2  (1)#0 e
2:  1  [r]   2    *  (0)#1 1^e
atlas>


If we again look at the block of the trivial

atlas> set B=block_of (trivial (G))
Variable B: [Param]
atlas> set show([Param] params)= void: for p in params do prints(p) od
Added definition  of show: ([Param]->)
atlas> show(B)
final parameter (x=0,lambda=/1,nu=/1)
final parameter (x=1,lambda=/1,nu=/1)
final parameter (x=2,lambda=/1,nu=/1)
atlas>


We focus on the first two elements:

atlas> B
Value: final parameter (x=0,lambda=/1,nu=/1)
atlas> B
Value: final parameter (x=1,lambda=/1,nu=/1)
atlas>


Remark: There are two commands that give us discrete series directly. For other groups with more representations it is more helpful to list them directly. See the example of $$Sp(4,R)$$ in the next section.

Recall that these are the (discrete series) representations associated to the compact Cartan subgroup. Note that they both have Harish-Chandra parameter lambda=rho. This is because the software is using a different x. Remember that we have to fix a KGB element x_b to fix a real group $$K$$. Let us fix it to be x=0:

atlas> set x_b=KGB(G,0)
Variable x_b: KGBElt
atlas> x_b
Value: KGB element #0
atlas>


Now, in order to identify the representation associated to x=1 with a representation associated to x=0, we need to conjugate x=1 to x=0. This will conjugate lambda to -lambda. Then the harish chandra parameters of the discrete series with respect to the fixed element x=0 will be:

atlas> hc_parameter(B,x_b)
Value: [ 1 ]/1
atlas> hc_parameter(B,x_b)
Value: [ -1 ]/1
atlas>


So, one is the holomorphic discrete series and the other is the anti-holomorphic one. But by choosing x_b =1` we get the opposite situation for the Harish Chandra parameters and holomorphic convention.