function [bonds,status] = EBTF_cause(bonds);
% EBTF_cause - causality for a EBTF component
% 
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%     %%%%% Model Transformation Tools %%%%%
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% 
% Matlab function  EBTF_cause
% [bonds,status] = EBTF_cause(bonds)

%SUMMARY EBTF: transformer component - bicausal on effort
%DESCRIPTION Energy conserving two-port
%DESCRIPTION e_1 f_1 = e_2 f_2 and e_1 and e_2 are both imposed.


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% % Version control history
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% % $Id$
% % $Log$
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% Copyright (c) P.J. Gawthrop, 1998.

% Check that there are exactly two bonds.
if check_bonds(bonds,2,'EBTF')==0
  return
end

% Effort must be imposed by both bonds
if (bonds(1,1)==-1)|(bonds(2,1)==-1) % Overcausal
  status = 1;
  return
end;

bonds(1,1) = 1; 
bonds(2,1) = 1;

% Flow bond must have through causality
if (bonds(1,2)==0)&(bonds(2,2)==0) % Undercausal
  status = -1;
  return
end;

if (bonds(1,2)==bonds(2,2))&(bonds(1,2)!=0) % Overcausal
  status = 1;
  return
end;

%Set flow causality
if (bonds(1,2)!=0)
  bonds(2,2) = -bonds(1,2)
else
  bonds(1,2) = -bonds(2,2)
end;
  
status = 0;

function  structure = EBTF_eqn(name,bond_number,bonds,direction,cr,args, ...
                            structure,eqnfile);

if nargin<8
  eqnfile = 'stdout';
end;

% Check that there are exactly two bonds.
if check_bonds(bonds,2,'EBTF')==0
  return
end

% There are 2 ports; extract the information
e_1 = bonds(1,1);
f_1 = bonds(1,2);
e_2 = bonds(2,1);
f_2 = bonds(2,2);


% Effort -- no equation

% Flow
effort1_name = varname(name,bond_number(1), 1);
effort2_name = varname(name,bond_number(2), 1);
flow1_name = varname(name,bond_number(1), -1);
flow2_name = varname(name,bond_number(2), -1);

if f_1==-1 %Write flow on port 2
  fprintf(eqnfile,'%s := (%s/%s)*%s;\n' , ...
      flow2_name, ...
      effort1_name, ...
      effort2_name, ...
      flow1_name);
else %Write flow on port 1
  fprintf(eqnfile,'%s := (%s/%s)*%s;\n' , ...
      flow1_name, ...
      effort2_name, ...
      effort1_name, ...
      flow2_name);
end;