def GetExpTrajectoriesFromOutput( celltype_name ,
                                 biocellion_output_file, Ngenes ):
    """ Extract gene expression trajectory from simulation 
    celltype_name   : Name of the cell type {BN_0, BN_1, BN_2, BN_3, BN_4}
    biocellion_output_file : File printed by the biocellion model of PDAC
    Ngenes : Number of genes.
    """
    gene_expression = []
    
    with open(biocellion_output_file, 'r') as bcfile :
        genecount = [ 0 for x in range(Ngenes) ]
        cont = 0
        for line in bcfile :
            if celltype_name in line :
                genesum = int(  line.strip().split(":")[-1] )
                genecount[ cont ] = genesum
                cont =  cont + 1

            if ( cont == Ngenes ) :
                gene_expression.append( genecount )
                genecount = [ 0 for x in range( Ngenes ) ]
                cont = 0
     
    return gene_expression