diff_ctr.m

高等引用数学的matlab求解的配套程序

      function [dy,dx]=diff_ctr(y, Dt, n)
      yx1=[y 0 0 0 0 0]; yx2=[0 y 0 0 0 0]; yx3=[0 0 y 0 0 0];
      yx4=[0 0 0 y 0 0]; yx5=[0 0 0 0 y 0]; yx6=[0 0 0 0 0 y];
      switch n
      case 1
         dy = (-diff(yx1)+7*diff(yx2)+7*diff(yx3)-diff(yx4))/(12*Dt); L0=3;
      case 2
         dy=(-diff(yx1)+15*diff(yx2)-15*diff(yx3)+diff(yx4))/(12*Dt^2);L0=3;
      case 3
         dy=(-diff(yx1)+7*diff(yx2)-6*diff(yx3)-6*diff(yx4)+...
               7*diff(yx5)-diff(yx6))/(8*Dt^3); L0=5;
      case 4
         dy = (-diff(yx1)+11*diff(yx2)-28*diff(yx3)+28*diff(yx4)-...
            11*diff(yx5)+diff(yx6))/(6*Dt^4);L0=5;
      end
      dy=dy(L0+1:end-L0); dx=([1:length(dy)]+L0-2-(n>2))*Dt;
%      dy=dy(L0+1:end-L0); dx=[0:length(dy)-1]*Dt;