ssts__tether_mmet_ii_discrete_number_sfunction_ii.m

空间绳系卫星的仿真软件

function [sys,x0,str,ts] = SSTS__tether_MMET_II_discrete_number_sfunction_II(t,x,u,flag)

% /*M-FILE Function SSTS__tether_MMET_II_discrete_number_sfunction_II MMM SSTSLAB */
% /*==================================================================================================
%  Simple Space Tether Simulation Laboratory Toolbox for Matlab 7.x
%
%  Copyright 2007 The SxLAB Family - Yi Chen - [e-mail]
% ====================================================================================================
%File description:
%  this sfunction is to calculate the sum from 1~N ( MMET-II discrete point masses )
% 
%                   2*idx - 1
%     ___________________________________ _ 
% 
%     ( R^2 - (2*idx-1)*R*L*cos(psi)/N +
%     ((2*idx-1)*L/2/N))^2  )^(3/2);
%                     
%                   2*idx - 1
%     ___________________________________  
% 
%     ( R^2 + (2*idx-1)*R*L*cos(psi)/N +
%     ((2*idx-1)*L/2/N))^2  )^(3/2);
% 
%Input:
%
%   t -- time                                         [Not modify]
%   x -- state of s funciton                          [Not modify]
%   u -- inputs vector , where                        [by user]
%               u(1) -- N, number of point masses ( 20 in default)
%               u(2) -- R, radius of orbit
%               u(3) -- L,length of tether
%               u(4) -- psi, rotate angle in plane of tether
%   flag -- flat status                               [No modify]
%
%Output:
%   sys -- outputs vector        [by user]
%   x0  -- sfunction std output  [Not modify]
%   str -- sfunction std output  [Not modify]
%   ts  -- sfunction std output  [Not modify]
%
% Appendix comments:
%  follow the example of timestwo.m, provide by matlab
%
% Usage:
%
%
%===================================================================================================
%  See Also:         SSTS__tether_MMET_II_discrete_number_sfunction_I
%                    SSTS__tether_MMET_II_discrete_number_sfunction_II
%                    SSTS__tether_MMET_II_discrete_number_sfunction_III
%
%===================================================================================================
%
%===================================================================================================
%Revision -
%Date        Name    Description of Change email                 Location
%22-Dec-2006 Chen Yi Initial               [e-mail]  Glasgow
%HISTORY$
%==================================================================================================*/

% SSTS__tether_MMET_II_discrete_number_sfunction_II Begin

% The following outlines the general structure of an S-function.
%

switch flag,

    case 0,
        [sys,x0,str,ts] = mdlInitializeSizes;

    case 3
        sys=mdlOutputs(t,x,u);

        %%%%%%%%%%%%%%%%%%%
        % Unhandled flags %
        %%%%%%%%%%%%%%%%%%%
        % There are no termination tasks (flag=9) to be handled.
        % Also, there are no continuous or discrete states,
        % so flags 1,2, and 4 are not used, so return an emptyu
        % matrix
    case { 1, 2, 4, 9 }
        sys=[];

    otherwise
        error(['Unhandled flag = ',num2str(flag)]);

end

% SSTS__tether_MMET_II_discrete_number_sfunction_II End


%=============================================================================
% mdlInitializeSizes
% Return the sizes, initial conditions, and sample times for the S-function.
%=============================================================================
%
function [sys,x0,str,ts]=mdlInitializeSizes
sizes = simsizes;
sizes.NumContStates  = 0;
sizes.NumDiscStates  = 0;  % x
sizes.NumOutputs     = 1;  % sys
sizes.NumInputs      = 4;  % u
sizes.DirFeedthrough = 1;  %  if 0, not direct feedthrough, we need have flag = 2
%  if 1, has direct feedthrough, we dont need
%  flag = 2 ,
sizes.NumSampleTimes = 1;   % at least one sample time is needed

sys = simsizes(sizes);

str = [];     % str is always an empty matrix
x0  = []; % initialize the initial conditions
ts  = [-1 0]; % inherited sample time ,initialize the array of sample times
% end mdlInitializeSizes


%=============================================================================
% mdlOutputs
% Return the output vector for the S-function
%=============================================================================
%
function sys = mdlOutputs(t,x,u);
[sys] =sum_point_mass(u);
%               u(1) -- N, number of point masses ( 20 in default)
%               u(2) -- R, radius of orbit
%               u(3) -- L,length of tether
%               u(4) -- psi, rotate angle in plane of tether
% end mdlOutputs

function  [ sum_mass] = sum_point_mass( u )
%               u(1) -- N, number of point masses ( 20 in default)
%               u(2) -- R, radius of orbit
%               u(3) -- L,length of tether
%               u(4) -- psi, rotate angle in plane of tether

sum_mass = 0;

    for idx = 1 : 1 : u(1)
        
        sum_mass = sum_mass + ...
( ( ( u(2)^2 - (2*idx-1)*u(2)*u(3)*cos(u(4))/u(1) + ((2*idx-1)*u(3)/2/u(1))^2  )^(-3/2) - ...
   ( u(2)^2 + (2*idx-1)*u(2)*u(3)*cos(u(4))/u(1) + ((2*idx-1)*u(3)/2/u(1))^2  )^(-3/2) )*...
   ( 2*idx - 1 ) ) ;

    end