Load grid and calculate alpha values from the coverage/2.5.

def load_grid(self, alpha):
        '''Load grid and calculate alpha values from the coverage/2.5.
        '''
        grid = CRGrid.crt_grid(self.dirs[0] + '/grid/elem.dat',
                               self.dirs[0] + '/grid/elec.dat')
        self.plotman = CRPlot.plotManager(grid=grid)

        name = self.dirs[0] + '/inv/coverage.mag'
        content = np.genfromtxt(name, skip_header=1,
                                skip_footer=1, usecols=([2]))
        abscov = np.abs(content)
        if alpha:
            normcov = np.divide(abscov, 2.5)
            normcov[np.where(normcov > 1)] = 1
            mask = np.subtract(1, normcov)
            self.alpha = self.plotman.parman.add_data(mask)
        else:
            self.alpha = self.plotman.parman.add_data(np.ones(len(abscov)))