[clarify] Clarify graphing question

I am having difficulty graphing my results in Clarify.   I have tried various versions of code. What I what to do is first have on the xaxis are ideology scores going from -1 to 1.  I am doing a pooled logit with a large number of observations and I want to analyze vote choice based on ideology and region.   Here is my code. I tried various iterations of this and it keeps telling me "a is an invalid name"   estsimp logit vote core ideology1 generate plo = . generate phi = . generate xaxis = _n -2 in 1/2 (I alternatively tried putting the number of observations in here which is 69000). setx core 1 local a = -1 while `a' <= 1 (I have also tried this with other numbers) {  setx ideology1 'a' simqi, prval(1) genpr(pi) _pctile pi, p(2.5,97.5) replace plo = r(r1) if xaxis==`a' replace phi = r(r2) if xaxis==`a' drop pi local a = `a' - 1  (I have also tried this with +1) }   Thank you for your assistance.