% 

% Call:  [X, info {, perf {, D}}] = ucminf(fun,par, x0, opts {,D0})

%

% Input parameters

% fun  :  String with the name of the function.

% par  :  Parameters of the function.  May be empty.

% x0   :  Starting guess for  x .

% opts :  Vector with 4 elements:

%         opts(1) :  Expected length of initial step

%         opts(2:4)  used in stopping criteria:

%             ||g||_inf <= opts(2)                     or 

%             ||dx||_2 <= opts(3)*(opts(3) + ||x||_2)  or

%             no. of function evaluations exceeds  opts(4) . 

%         Any illegal element in  opts  is replaced by its

%         default value,  [1  1e-4*||g(x0)||_inf  1e-8  100]

% D0   :  (optional)  If present, then approximate inverse Hessian

%         at  x0 .  Otherwise, D0 := I 

% Output parameters

% X    :  If  perf  is present, then array, holding the iterates

%         columnwise.  Otherwise, computed solution vector.

% info :  Performance information, vector with 6 elements:

%         info(1:3) = final values of [f(x)  ||g||_inf  ||dx||_2] 

%         info(4:5) = no. of iteration steps and evaluations of (F,g)

%         info(6) = 1 :  Stopped by small gradient

%                   2 :  Stopped by small x-step

%                   3 :  Stopped by  opts(4) .

%                   4 :  Stopped by zero step.

% perf :  (optional). If present, then array, holding 

%          perf(1:2,:) = values of  f(x) and ||g||_inf

%          perf(3:5,:) = Line search info:  values of  

%                        alpha, phi'(alpha), no. fct. evals. 

%          perf(6,:)   = trust region radius.

% D    :  (optional). If present, then array holding the 

%         approximate inverse Hessian at  X(:,end) .



%  Hans Bruun Nielsen,  IMM, DTU.  00.12.18 / 02.01.22



  % Check call 

  [x n F g] = check(fun,par,x0,opts);

  if  nargin > 4,  D = checkD(n,D0);  fst = 0;

  else,            D = eye(n);  fst = 1;    end

  %  Finish initialization

  k = 1;   kmax = opts(4);   neval = 1;   ng = norm(g,inf);

  Delta = opts(1);

  Trace = nargout > 2;

  if  Trace

        X = x(:)*ones(1,kmax+1);

        perf = [F; ng; zeros(3,1); Delta]*ones(1,kmax+1);

      end

  found = ng <= opts(2);      

  h = zeros(size(x));  nh = 0;

  ngs = ng * ones(1,3);

   

  while  ~found

    %  Previous values

    xp = x;   gp = g;   Fp = F;   nx = norm(x);

    ngs = [ngs(2:3) ng];

    h = D*(-g(:));   nh = norm(h);   red = 0; 

    if  nh <= opts(3)*(opts(3) + nx),  found = 2;  

    else

      if  fst | nh > Delta  % Scale to ||h|| = Delta

        h = (Delta / nh) * h;   nh = Delta;   

        fst = 0;  red = 1;

      end

      k = k+1;

      %  Line search

      [al  F  g  dval  slrat] = softline(fun,par,x,F,g, h);

      if  al < 1  % Reduce Delta

        Delta = .35 * Delta;

      elseif   red & (slrat > .7)  % Increase Delta

        Delta = 3*Delta;      

      end 

      %  Update  x, neval and ||g||

      x = x + al*h;   neval = neval + dval;  ng = norm(g,inf);

      if  Trace

             X(:,k) = x(:); 

             perf(:,k) = [F; ng; al; dot(h,g); dval; Delta]; end

      h = x - xp;   nh = norm(h);

      if  nh == 0,

        found = 4; 

      else

        y = g - gp;   yh = dot(y,h);

        if  yh > sqrt(eps) * nh * norm(y)

          %  Update  D

          v = D*y(:);   yv = dot(y,v);

          a = (1 + yv/yh)/yh;   w = (a/2)*h(:) - v/yh;

          D = D + w*h' + h*w';

        end  % update D

        %  Check stopping criteria

        thrx = opts(3)*(opts(3) + norm(x));

        if      ng <= opts(2),              found = 1;

        elseif  nh <= thrx,                 found = 2;

        elseif  neval >= kmax,              found = 3; 

%        elseif  neval > 20 & ng > 1.1*max(ngs), found = 5;

        else,   Delta = max(Delta, 2*thrx);  end

      end  

    end  % Nonzero h

  end  % iteration



  %  Set return values

  if  Trace

    X = X(:,1:k);   perf = perf(:,1:k);

  else,  X = x;  end

  info = [F  ng  nh  k-1  neval  found];



% ==========  auxiliary functions  =================================



function  [x,n, F,g, opts] = check(fun,par,x0,opts0)

% Check function call

  x = x0(:);   sx = size(x);   n = max(sx);   

  if  (min(sx) > 1)

      error('x0  should be a vector'), end

  [F g] = feval(fun,x,par);

  sf = size(F);   sg = size(g);

  if  any(sf-1) | ~isreal(F)

      error('F  should be a real valued scalar'), end

  if  (min(sg) ~= 1) | (max(sg) ~= n)

      error('g  should be a vector of the same length as  x'), end

  so = size(opts0);

  if  (min(so) ~= 1) | (max(so) < 4) | any(~isreal(opts0(1:4)))

      error('opts  should be a real valued vector of length 4'), end

  opts = opts0(1:4);   opts = opts(:).';

  i = find(opts <= 0);

  if  length(i)    % Set default values

    d = [1  1e-4*norm(g, inf)  1e-8  100];

    opts(i) = d(i);

  end   

% ----------  end of  check  ---------------------------------------



function  D = checkD(n,D0)

% Check given inverse Hessian

  D = D0;   sD = size(D);

  if  any(sD - n)

      error(sprintf('D  should be a square matrix of size %g',n)), end

  % Check symmetry

  dD = D - D';   ndD = norm(dD(:),inf);

  if  ndD > 10*eps*norm(D(:),inf)

      error('The given D0 is not symmetric'), end

  if  ndD,  D = (D + D')/2; end  % Symmetrize      

  [R p] = chol(D);

  if  p

      error('The given D0 is not positive definite'), end

    

function  [alpha,fn,gn,neval,slrat] = ...
              softline(fun,fpar, x,f,g, h)

% Soft line search:  Find  alpha = argmin_a{f(x+a*h)}

  % Default return values 

  alpha = 0;   fn = f;   gn = g;   neval = 0;  slrat = 1;

  n = length(x);  

  

  % Initial values

  dfi0 = dot(h,gn);  if  dfi0 >= 0,  return, end

  fi0 = f;    slope0 = .05*dfi0;   slopethr = .995*dfi0;

  dfia = dfi0;   stop = 0;   ok = 0;   neval = 0;   b = 1;

  

  while   ~stop

    [fib g] = feval(fun,x+b*h,fpar);  neval = neval + 1;

    dfib = dot(g,h); 

    if  b == 1, slrat = dfib/dfi0; end

    if  fib <= fi0 + slope0*b    % New lower bound

      if  dfib > abs(slopethr),  stop = 1;

      else

        alpha = b;   fn = fib;   gn = g;   dfia = dfib;  

        ok = 1;   slrat = dfib/dfi0;

        if  (neval < 5) & (b < 2) & (dfib < slopethr)

          % Augment right hand end

          b = 2*b;

        else,  stop = 1; end

      end

    else,  stop = 1; end   

  end

  

  stop = ok;  xfd = [alpha fn dfia; b fib dfib; b fib dfib];

  while   ~stop

    c = interpolate(xfd,n);

    [fic g] = feval(fun, x+c*h, fpar);   neval = neval+1;

    xfd(3,:) = [c  fic  dot(g,h)];

    if fic < fi0 + slope0*c    % New lower bound

      xfd(1,:) = xfd(3,:);   ok = 1;

      alpha = c;   fn = fic;   gn = g;  slrat = xfd(3,3)/dfi0;

    else,  xfd(2,:) = xfd(3,:);  ok = 0; end

    % Check stopping criteria

    ok = ok & abs(xfd(3,3)) <= abs(slopethr);

    stop = ok | neval >= 5 | diff(xfd(1:2,1)) <= 0;

  end  % while   

%------------  end of  softline  ------------------------------

  

function  alpha = interpolate(xfd,n);

% Minimizer of parabola given by

% xfd(1:2,1:3) = [a fi(a) fi'(a); b fi(b) dummy]



  a = xfd(1,1);   b = xfd(2,1);   d = b - a;   dfia = xfd(1,3);

  C = diff(xfd(1:2,2)) - d*dfia;

  if C >= 5*n*eps*b    % Minimizer exists

    A = a - .5*dfia*(d^2/C);

    d = 0.1*d;   alpha = min(max(a+d, A), b-d);

  else

    alpha = (a+b)/2;

  end

%------------  end of  interpolate  --------------------------