def style_chg_ref(self,ref,symb=None,edc=None,fac=None,smbsz=None,edw=None,lab=None):
        '''
        This routine changes the plotting style that is set by default.
        The style is changed according the the reference of the paper
        as given in the grain database. For change according to type of
        grain, use the routine syle_chg_label().

        ['Symbol', 'Edge color', 'Face color', 'Symbol size', 'Edge width'
        ,'Label']

        You can see the current styles by running

        Attention: You have to give values to all variables that are
        compatible with the python mathplotlib. If not, it's your fault
        if nothing works.

        g.style

        Parameters
        ----------
        ref : string
            Select the reference of the grains you want to change.
        symb : string, optional
            Select new symbol. None for no change.
        edc : string, optional
            Select new edge color. None for no change.
        fac : string, optional
            Select new face color. None for no change.
        smbsz : string, optional
            Select new symbol size. None for no change.
        edw : string, optional
            Select new edge width. None for no change.
        lab : string, optional
            Select new label. None for no change.
        '''

        # do stuff for selected reference
        for i in range(len(self.style)):
            # check if reference is correct, otherwise continue directly
            if self.desc[i][self.descdict['Reference']] == ref:
                # change symbol:
                if symb != None:
                    self.style[i][self.styledict['Symbol']] = symb
                # change edge color
                if edc != None:
                    self.style[i][self.styledict['Edge color']] = edc
                # change face color
                if fac != None:
                    self.style[i][self.styledict['Face color']] = fac
                # change symbol size
                if smbsz != None:
                    self.style[i][self.styledict['Symbol size']] = smbsz
                # change edge width
                if edw != None:
                    self.style[i][self.styledict['Edge width']] = edw
                # change label
                if lab != None:
                    self.style[i][self.styledict['Label']] = lab