% Boyd, Kim, Vandenberghe, and Hassibi, "A tutorial on geometric programming"
% Joshi, Boyd, and Dutton, "Optimal doping profiles via geometric programming"
% Written for CVX by Almir Mutapcic 02/08/06
% (a figure is generated)
%
% Determines the optimal doping profile that minimizes base transit
% time in a (homojunction) bipolar junction transistor.
% This problem can be posed as a GP:
%
%   minimize   tau_B
%       s.t.   Nmin <= v <= Nmax
%              y_(i+1) + v_i^const1 <= y_i
%              w_(i+1) + v_i^const2 <= w_i, etc...
%
% where variables are v_i, y_i, and w_i.

% discretization size
M = 50;
% M = 1000; % takes a few minutes to process constraints

% problem constants
g1 = 0.42;
g2 = 0.69;
Nmax = 5*10^18;
Nmin = 5*10^16;
Nref = 10^17;
Dn0 = 20.72;
ni0 = 1.4*(10^10);
WB = 10^(-5);
C =  WB^2/((M^2)*(Nref^g1)*Dn0);

% exponent powers
pwi = g2 -1;
pwj = 1+g1-g2;

% optimization variables
cvx_begin gp
  variables v(M) y(M) w(M)

  % objective function is the base transmit time
  tau_B = C*w(1);

  minimize( tau_B )
  subject to
    % problem constraints
    v >= Nmin;
    v <= Nmax;

    for i = 1:M-1
      if( mod(i,100) == 0 ), fprintf(1,'progress counter: %d\n',i), end;
      y(i+1) + v(i)^pwj <= y(i);
      w(i+1) + y(i)*v(i)^pwi <= w(i);
    end

    y(M) == v(M)^pwj;
    w(M) == y(M)*v(M)^pwi;
cvx_end

% plot the basic optimal doping profile
figure, clf
nbw = 0:1/M:1-1/M;
semilogy(nbw,v,'LineWidth',2);
axis([0 1 1e16 1e19]);
xlabel('base');
ylabel('doping');
text(0,Nmin,'Nmin ', 'HorizontalAlignment','right');
text(0,Nmax,'Nmax ', 'HorizontalAlignment','right');
disp('Optimal doping profile is plotted.')

 
Calling Mosek 9.1.9: 785 variables, 343 equality constraints
   For improved efficiency, Mosek is solving the dual problem.
------------------------------------------------------------

MOSEK Version 9.1.9 (Build date: 2019-11-21 11:32:15)
Copyright (c) MOSEK ApS, Denmark. WWW: mosek.com
Platform: MACOSX/64-X86

Problem
  Name                   :                 
  Objective sense        : min             
  Type                   : CONIC (conic optimization problem)
  Constraints            : 343             
  Cones                  : 196             
  Scalar variables       : 785             
  Matrix variables       : 0               
  Integer variables      : 0               

Optimizer started.
Presolve started.
Linear dependency checker started.
Linear dependency checker terminated.
Eliminator started.
Freed constraints in eliminator : 47
Eliminator terminated.
Eliminator started.
Freed constraints in eliminator : 0
Eliminator terminated.
Eliminator - tries                  : 2                 time                   : 0.00            
Lin. dep.  - tries                  : 1                 time                   : 0.00            
Lin. dep.  - number                 : 0               
Presolve terminated. Time: 0.00    
Problem
  Name                   :                 
  Objective sense        : min             
  Type                   : CONIC (conic optimization problem)
  Constraints            : 343             
  Cones                  : 196             
  Scalar variables       : 785             
  Matrix variables       : 0               
  Integer variables      : 0               

Optimizer  - threads                : 8               
Optimizer  - solved problem         : the primal      
Optimizer  - Constraints            : 294
Optimizer  - Cones                  : 196
Optimizer  - Scalar variables       : 736               conic                  : 588             
Optimizer  - Semi-definite variables: 0                 scalarized             : 0               
Factor     - setup time             : 0.00              dense det. time        : 0.00            
Factor     - ML order time          : 0.00              GP order time          : 0.00            
Factor     - nonzeros before factor : 1383              after factor           : 1545            
Factor     - dense dim.             : 0                 flops                  : 2.06e+04        
ITE PFEAS    DFEAS    GFEAS    PRSTATUS   POBJ              DOBJ              MU       TIME  
0   1.6e+00  2.0e+01  4.3e+02  0.00e+00   -4.271448072e+02  0.000000000e+00   1.0e+00  0.00  
1   4.5e-01  5.4e+00  9.7e+01  -5.62e-03  -2.010492860e+02  -1.725419645e+01  2.8e-01  0.01  
2   1.3e-01  1.6e+00  1.8e+01  5.38e-01   -9.319749265e+01  -2.879246268e+01  8.1e-02  0.01  
3   2.9e-02  3.5e-01  1.3e+00  9.94e-01   -4.392050527e+01  -3.111037320e+01  1.8e-02  0.01  
4   7.9e-03  9.6e-02  1.7e-01  1.58e+00   -2.730920243e+01  -2.460249031e+01  4.9e-03  0.01  
5   3.7e-03  4.5e-02  5.6e-02  1.18e+00   -2.501399990e+01  -2.381274311e+01  2.3e-03  0.02  
6   1.4e-03  1.7e-02  1.3e-02  1.09e+00   -2.383565001e+01  -2.340201373e+01  8.6e-04  0.02  
7   3.4e-04  4.1e-03  1.5e-03  1.04e+00   -2.332141823e+01  -2.321680161e+01  2.1e-04  0.02  
8   4.2e-05  5.0e-04  6.5e-05  1.01e+00   -2.316897429e+01  -2.315622426e+01  2.6e-05  0.02  
9   4.8e-06  5.9e-05  2.6e-06  1.00e+00   -2.314960657e+01  -2.314812364e+01  3.0e-06  0.02  
10  7.4e-07  8.9e-06  1.5e-07  1.00e+00   -2.314744030e+01  -2.314721524e+01  4.6e-07  0.02  
11  2.0e-07  2.4e-06  2.1e-08  1.00e+00   -2.314715833e+01  -2.314709779e+01  1.2e-07  0.02  
12  2.6e-08  5.6e-08  7.6e-11  1.00e+00   -2.314705656e+01  -2.314705514e+01  2.9e-09  0.02  
13  1.5e-09  3.2e-09  1.0e-12  1.00e+00   -2.314705423e+01  -2.314705415e+01  1.6e-10  0.02  
Optimizer terminated. Time: 0.03    


Interior-point solution summary
  Problem status  : PRIMAL_AND_DUAL_FEASIBLE
  Solution status : OPTIMAL
  Primal.  obj: -2.3147054228e+01   nrm: 3e+00    Viol.  con: 1e-09    var: 1e-10    cones: 0e+00  
  Dual.    obj: -2.3147054147e+01   nrm: 2e+01    Viol.  con: 0e+00    var: 9e-10    cones: 0e+00  
Optimizer summary
  Optimizer                 -                        time: 0.03    
    Interior-point          - iterations : 13        time: 0.02    
      Basis identification  -                        time: 0.00    
        Primal              - iterations : 0         time: 0.00    
        Dual                - iterations : 0         time: 0.00    
        Clean primal        - iterations : 0         time: 0.00    
        Clean dual          - iterations : 0         time: 0.00    
    Simplex                 -                        time: 0.00    
      Primal simplex        - iterations : 0         time: 0.00    
      Dual simplex          - iterations : 0         time: 0.00    
    Mixed integer           - relaxations: 0         time: 0.00    

------------------------------------------------------------
Status: Solved
Optimal value (cvx_optval): +1.57873e-12
 
Optimal doping profile is plotted.