function [m,n,OPERATIONS,E,d] = ppriori(A)

% PPRIORI Priority entry of matrix of polynomials in long format. 
%	[m,n,OPERATIONS] = PPRIORI(A) returns the indices m and n of
%	the priority entry in A and a third output, OPERATIONS, for use 
%       with PALGO, PALGO2 and PQUICK to determine the type of operation 
%	to be performed.
%	
%	[m,n,OPERATIONS,E,d] = PPRIORI(A) returns the numerator and the 
%	denominator of the priority entry value of matrix A.
%
%	Possible OPERATIONS are:
% 	1 corresponds to a row operation.
% 	2 corresponds to a column operation.
%
%	See also PRIORITY
  
%	Adapted from Harold M. Edwards, "Linear Algebra."
%	Written by Serge Tchikanda 06/13/95.
%       Last revised by Serge Tchikanda 06/18/96.

[M,N]=psize(A);
if isempty(M) | isempty(N)
   return
end
U = ptriu(A,1);			% Upper triangular part of A
L = ptril(A,-1);		% Lower triangular part of A

idxu=pfind(U);
idxl=pfind(L);

if ~any(idxu) & ~any(idxl) & nargout > 3		
    disp('  ')                          % If entries in U and L are all 
    disp('No priority entry found')     % zeroes, then A is diagonal and
    disp('Matrix is diagonal')          % thus has no priority entry.
    return  					 
else    
    [i1,j1] = pfind(U);			% Find nonzero entries in U	
    mU = min(i1);			% Find priority entry (mU,nU)
    nU = max(pfind(prtv(U,mU,':')));	% in U.

    [i2,j2] = pfind(L);			% Find nonzero entries in L
    nL = min(j2);			% Find priority entry (mL,nL)	
    mL = max(pfind(prtv(L,':',nL)));	% in L 
   
    if (isempty(i1)) & (isempty(j1))		% If no nonzero entry in U,
	OPERATIONS = 1;			% priority entry (m,n) of A
	m = mL;				% must be in L.
	n = nL;				

    elseif (isempty(i2)) & (isempty(j2))	% If no nonzero entry in L,
	OPERATIONS = 2;			% priority entry (m,n) of A
        m = mU;				% must be in U.
        n = nU;

    else				% Else, there are nonzero entries 
					% in both U an L.

        if mU <= nL			% If row index in U less than or equal 	
	   OPERATIONS = 2;		% to column index in L, then priority
	   m = mU;			% entry is in U.
	   n = nU;

        else				% If row index in U greater than
	   OPERATIONS = 1;		% column index in L, then priority
 	   m = mL;			% entry is in L.
	   n = nL;
        end
     end 
end
[E,d] = gpet(A,m,n);