function [a,b] = regcon(mod,xmn,ymn,xst,yst);
%REGCON Converts regression model to y = ax + b form
% REGCON can be used to convert a model (mod) generated by the
% the function MODLMKER or MODLGUI. The outputs are the
% regression coefficients (a) and the intercept (b)
% such that y = ax + b. In this case the I/O syntax is:
%
% [a,b] = regcon(mod);
%
% REGCON can also be used to convert the individual parts of a
% regression model, including the column vector of regression
% coefficients (regv), predictor variable means (xmn), 
% predicted variable means (ymn), predictor variable scaling 
% (xst), and predicted variable scaling (yst).  If xmn or ymn 
% is not supplied or is set equal to 0 or [], then it is assumed 
% to be zero (i.e. no centering was used in the model). If xst 
% or yst is not supplied or is set equal to 0 or [], then it is 
% assumed to be one (i.e. no scaling was used in the model). 
% In this case the I/0 syntax is:
%
% [a,b] = regcon(regv,xmn,ymn,xst,yst);
%
% Examples:
% [a,b] = regcon(mod);                  % using MODLMKER model
% [a,b] = regcon(regv,xmn,ymn);         % mean centered only
% [a,b] = regcon(regv,xmn,ymn,xst,yst); % mean centered and scaled
% [a,b] = regcon(regv,xmn,ymn,[],yst);  % x data centered but not scaled
% [a,b] = regcon(regv,0,0,xst,yst);     % x and y scaled by not centered
%
%  See also MODLPRED, MODLRDER, MODLMKER, MODLGUI, MODLPARS,
%  PLS, CONPRED1, PCR, RIDGE, AUTO, MNCN

%  Copyright Eigenvector Research 1997
%  by BM Wise, July, 1997
if (nargin < 2 & any([mod(1,11) == 1  mod(1,11) == 2 mod(1,11) == 3]))
  [xmn,ymn,xst,yst,bb,p,w,tsq,q] = modlpars(mod);
  nxv = mod(1,8);
  nyv = mod(1,10);
else
  bb = mod;
  [nxv,nyv] = size(mod);
  if nargin == 1
    xmn = 0; ymn = 0; xst = 0; yst = 0;
  elseif nargin == 2
    ymn = 0; xst = 0; yst = 0;
  elseif nargin == 3
    xst = 0; yst = 0;
  elseif nargin == 4
    yst = 0;
  end
end
if (xmn == 0 | isempty(xmn))
  xmn = zeros(1,nxv);
end
if (xst == 0 | isempty(xst))
  xst = ones(1,nxv);
end
if (ymn == 0 | isempty(ymn))
  ymn == zeros(1,nyv);
end
if (yst == 0 | isempty(yst))
  yst = ones(1,nyv);
end

b = -((xmn./xst)*bb).*yst + ymn;
a = diag(yst)*(bb'./xst(ones(nyv,1),:));