title 'Response surface with a single optimum';
data response;
input T Ti A yield;
label 
T = "Temperature"
Ti = "Time"
A = "Acid";
datalines;
121 3 0 3.55
108 3 0 57.61
121 1 0 60.77
108 1 0 59.8
121 2 0 64.72
108 2 0 63.48
121 3 1 70.56
108 3 1 58.24
121 1 1 63.58
108 1 1 61.6
121 2 1 57.8
108 2 1 59.56
121 3 2 63.98
108 3 2 61.51
121 1 2 73.4
108 1 2 62.6
121 2 2 63.34
108 2 2 58.6
;
proc print data = response;
run; quit;
proc rsreg data = response;
model yield = T Ti A/lackfit;
run;
ods graphics on;
proc rsreg data = response
           plots(only unpack)=surface(3d at(T=1.616673));
   model  yield = T Ti A;
   ods select 'T * A = Pred';
run;
ods graphics off;