def _kappaShapelets(self, shapelets, beta):
        """
        calculates the convergence kappa given lensing potential shapelet coefficients (laplacian/2)
        :param shapelets: set of shapelets [l=,r=,a_lr=]
        :type shapelets: array of size (n,3)
        :returns:  set of kappa shapelets.
        :raises: AttributeError, KeyError
        """
        output=np.zeros((len(shapelets)+1,len(shapelets)+1),'complex')
        for nl in range(0,len(shapelets)):
            for nr in range(0,len(shapelets)):
                a_lr=shapelets[nl][nr]
                if nl>0:
                    output[nl-1][nr+1]+=a_lr*np.sqrt(nl*(nr+1))/2
                    if nr>0:
                        output[nl-1][nr-1]+=a_lr*np.sqrt(nl*nr)/2
                output[nl+1][nr+1]+=a_lr*np.sqrt((nl+1)*(nr+1))/2
                if nr>0:
                    output[nl+1][nr-1]+=a_lr*np.sqrt((nl+1)*nr)/2
        return output/beta**2