function A = rcop(A,a,b,c,d)

% RCOP	Row column operations
%	A = RCOP(A,a,b,c,d) performs an operation on matrix A
% 	according to the following prescription:
%	If a = 1, add b times row c to row d. If a = 2, do a 
%	column operation.
%
%       A = RCOP(A,v) does the same thing with v = [a b c d].
%
%       See also UNIMOD, UNIMOD2, QUICK, QUICK2, ALGO, ALGO2,
%                RC_OP, MODIFY, AUTOMOD

%	Adapted from Harold M. Edwards, "Linear Algebra."
%	Written by Serge Tchikanda 02/14/96.
%       Last revised by Serge Tchikanda 02/24/96.

[mrows,ncols]=size(A);

if (nargin == 2) & (length(a) == 4)
   b = a(2);
   c = a(3);
   d = a(4);
   a = a(1);

elseif (nargin == 2 | nargin == 3) & (length(a) ~= 4)
   disp(' ')
   disp('   When using 2 input arguments, second input must')
   disp('   contain 4 elements. No operation was performed.')
   break  
end   

if a == 1

   if (c > mrows) | (d > mrows) | (c <= 0) | (d <= 0)
       disp(' ')
       str1=['    Invalid index specification. '];
       str2=['The matrix has ',int2str(mrows),' row(s).'];
       disp([str1 str2])
       disp('    No operation was performed.') 

   elseif (c == d)
       disp(' ')
       disp(['    Invalid index specification. Indices c and d must'])
       disp(['    be different. No operation was performed. '])

   else 
       A(d,:) = A(d,:) + b*A(c,:);

      str = [int2str(b),' times ','row ',int2str(c), ...
             ' was added to row ',int2str(d),'.'];
      disp(str)
   end

elseif a == 2

   if (c > ncols) | (d > ncols) | (c <= 0) | (d <= 0)
       disp(' ')
       str1=['    Invalid index specification. '];
       str2=['The matrix has ',int2str(ncols),' column(s).'];
       disp([str1 str2])
       disp('    No operation was performed.') 

   elseif (c == d)
       disp(' ')
       disp(['    Invalid index specification. Indices c and d must'])
       disp(['    be different. No operation was performed. '])

   else 
       A(:,d) = A(:,d) + b*A(:,c);

      str = [int2str(b),' times ','column ',int2str(c), ...
             ' was added to column ',int2str(d),'.'];
      disp(str) 
   end

else

   disp(' ')
   disp('    Invalid selection, index a must be 1 or 2.')
   disp('    No operation was performed.') 
end