classdef D2Standard < sbp.OpSet
    properties
        D1 % SBP operator approximating first derivative
        H % Norm matrix
        HI % H^-1
        Q % Skew-symmetric matrix
        e_l % Left boundary operator
        e_r % Right boundary operator
        D2 % SBP operator for second derivative
        M % Norm matrix, second derivative
        d1_l % Left boundary first derivative
        d1_r % Right boundary first derivative
        m % Number of grid points.
        h % Step size
        x % grid
        borrowing % Struct with borrowing limits for different norm matrices

    end

    methods
        function obj = D2Standard(m,lim,order)

            x_l = lim{1};
            x_r = lim{2};
            L = x_r-x_l;
            obj.h = L/(m-1);
            obj.x = linspace(x_l,x_r,m)';

            if order == 2
                [obj.H, obj.HI, obj.D1, obj.D2, obj.e_l,...
                obj.e_r, obj.M, obj.Q, obj.d1_l, obj.d1_r] =...
                sbp.implementations.d2_2(m,obj.h);
                obj.borrowing.M.S = 0.4000;
            elseif order == 4
                [obj.H, obj.HI, obj.D1, obj.D2, obj.e_l,...
                obj.e_r, obj.M, obj.Q, obj.d1_l, obj.d1_r] =...
                sbp.implementations.d2_4(m,obj.h);
                obj.borrowing.M.S = 0.2508;
            elseif order == 6
                [obj.H, obj.HI, obj.D1, obj.D2, obj.e_l,...
                obj.e_r, obj.M, obj.Q, obj.d1_l, obj.d1_r] =...
                sbp.implementations.d2_6(m,obj.h);
                obj.borrowing.M.S = 0.1878;
            elseif order == 8
                [obj.H, obj.HI, obj.D1, obj.D2, obj.e_l,...
                obj.e_r, obj.M, obj.Q, obj.d1_l, obj.d1_r] =...
                sbp.implementations.d2_8(m,obj.h);
                obj.borrowing.M.S = 0.0015;
            elseif order == 10
                [obj.H, obj.HI, obj.D1, obj.D2, obj.e_l,...
                obj.e_r, obj.M, obj.Q, obj.d1_l, obj.d1_r] =...
                sbp.implementations.d2_10(m,obj.h);
                obj.borrowing.M.S = 0.0351;
            elseif order == 12
                [obj.H, obj.HI, obj.D1, obj.D2, obj.e_l,...
                obj.e_r, obj.M, obj.Q, obj.d1_l, obj.d1_r] =...
                sbp.implementations.d2_12(m,obj.h);
                obj.borrowing.M.S = []; % Need to compute!
                warning('D2=D1*D1 (wide stencil).');
                warning('The borrowing constant has not been computed.')
            else
                error('Invalid operator order %d.',order);
            end

            obj.m = m;
        end

        function str = string(obj)
            str = [class(obj) '_' num2str(obj.order)];
        end

    end
end