function A = readPetscBinMat(filename)
% function A = readPetscBinMat(filename)
% read Petsc Binary format matrix (no support for imaginary numbers)
% 20.05.2003 Antti.Vanne@uku.fi

% MATRIX
%   int    MAT_FILE_COOKIE
%   int    number of rows
%   int    number of columns
%   int    total number of nonzeros
%   int    *number nonzeros in each row
%   int    *column indices of all nonzeros (starting index is zero)
%   PetscScalar *values of all nonzeros
  
  MAT_FILE_COOKIE = 1211216;
  
  fid = fopen(filename, 'r', 'b');
  
  cookie = fread(fid, 1, 'int');
  if (cookie ~= MAT_FILE_COOKIE)
    error('Not a petsc matrix file.');
  end
  
  M = fread(fid, 1, 'int');
  N = fread(fid, 1, 'int');
  totalNnz = fread(fid, 1, 'int');
  nnzrows = fread(fid, M, 'int');
  colInds = fread(fid, totalNnz, 'int');
  data = fread(fid, totalNnz, 'double');
  
  ci = 1; 
  rowInds = zeros(totalNnz, 1);
  h = waitbar(0, 'Constructing row indices');
  for row = 1:M
    waitbar(row/M, h);
    if (nnzrows(row) == 0), continue, end % no data in this row
    rowInds(ci:ci+nnzrows(row)-1) = row*ones(nnzrows(row), 1);
    ci = ci+nnzrows(row); 
  end
  close(h);
  A = sparse(rowInds, colInds+1, data);