Hello, I am working on fitting nonlinear mixed model to my data using proc nlmixed. My model has four fixed effects & five random effects. But when I run the program, I get the following warning: WARNING: The final Hessian matrix is full rank but has at least one negative eigenvalue. Second-order optimality condition violated. Please help me solve this problem and guide me to the right way to solve this problem. My code is the following and the data is in the attachment: proc import datafile='C:\Users\Abbas Arkawazi\Desktop\test.xlsx' DBMS =xlsx Out=test; run; proc nlmixed data=test ; parms b0=1 b1=2 b2=3 b3=4 a=2 b=1 aa=3 bb=1 s=100; m =b0+(b1*age)+(b2*creatin)+(b3*gender); y=urea; if status_u=1 then f=((aa*bb*a*b)/s)*(exp(-b*exp((y-m)/s)))*((1-exp(-b*exp((y-m)/s)))**(a-1))*((((1-exp(-b*exp((y-m)/s)))**a)**(aa-1))/((1-((1-exp(-b*exp((y-m)/s)))**a))**(aa+1)))*((1+((((1-exp(-b*exp((y-m)/s)))**a)/(1-((1-exp(-b*exp((y-m)/s)))**a)))**aa))**(-bb-1)) ; else f= 1-((1+(((1-exp(-b*exp((y-m)/s)))**a)/(1-(1-exp(-b*exp((y-m)/s)))**a))**aa)**-bb) ; ll=log(f); model y ~ general(ll); run;
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