matlab编写s函数,求解 【Matlab】Matlab中如何编写S函数
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mpl\u7684118\u884ccase 3,sys=mdlOutputs(t,x,u);flag=3\u8868\u793a\u6b64\u65f6\u8981\u8ba1\u7b97\u8f93\u51fa\uff0c\u5373y=fo(t,x,u),\u627e\u5230mdlOutputs\u51fd\u6570\uff08\u5728218\u884c\uff09\uff0c\u5982\u4e0a\uff0c\u5982\u679csys=[]\u8868\u793a\u6ca1\u6709\u8f93\u51fa\uff0c\u6211\u4eec\u6539\u6210sys=fo(t,x,u)\u6216sys=C*x+D*u %sys\u6b64\u65f6\u4e3a\u8f93\u51fay\u597d\u50cf\u5feb\u5b8c\u4e86\uff0c\u563b\u563b\uff0c\u5728sfuntmpl\u7684124\u884ccase 4,sys=mdlGetTimeOfNextVarHit(t,x,u);flag=4\u8868\u793a\u6b64\u65f6\u8981\u8ba1\u7b97\u4e0b\u4e00\u6b21\u91c7\u6837\u7684\u65f6\u95f4\uff0c\u53ea\u5728\u79bb\u6563\u91c7\u6837\u7cfb\u7edf\u4e2d\u6709\u7528(\u5373\u4e0a\u6587\u7684mdlInit ializeSizes\u4e2d\u63d0\u5230\u7684ts\u8bbe\u7f6ets(1)\u4e0d\u4e3a0)\u8fde\u7eed\u7cfb\u7edf\u4e2d\u53ea\u9700\u5728mdlGetTimeOfNextVarHit\u51fd\u6570\u4e2d\u5199\u4e0asys=[];\u8fd9\u4e2a\u51fd\u6570\u4e3b\u8981\u7528\u4e8e\u53d8\u6b65\u957f\u7684\u8bbe\u7f6e\uff0c\u5177\u4f53\u5b9e\u73b0\u5927\u5bb6\u53ef\u4ee5\u7528edit vsfunc\u770bvsfunc.m\u8fd9\u4e2a\u4f8b\u5b50\u6700\u540e\u4e00\u4e2a\uff0c\u5728sfuntmpl\u7684130\u884ccase 9,sys=mdlTerminate(t,x,u);flag=9\u8868\u793a\u6b64\u65f6\u7cfb\u7edf\u8981\u7ed3\u675f\uff0c\u4e00\u822c\u6765\u8bf4\u5199\u4e0a\u5728mdlTerminate\u51fd\u6570\u4e2d\u5199\u4e0asys=[]\u5c31\u53ef\uff0c\u5982\u679c\u4f60\u5728\u7ed3\u675f\u65f6\u8fd8\u8981\u8bbe\u7f6e\u4ec0\u4e48\uff0c\u5c31\u5728\u6b64\u51fd\u6570\u4e2d\u5199\u5173\u4e8esfuntmpl\u8fd9\u4e2as\u51fd\u6570\u7684\u6a21\u677f\u8bb2\u5b8c\u4e86\u3002s\u51fd\u6570\u8fd8\u53ef\u4ee5\u5e26\u7528\u6237\u53c2\u6570\uff0c\u4e0b\u9762\u7ed9\u4e2a\u4f8b\u5b50\uff0c\u548csimulink\u4e0b\u7684gain\u6a21\u5757\u529f\u80fd\u4e00\u6837\uff0c\u5927\u4f19\u81ea\u5df1 \u770b\u5427\uff0c\u6211\u7761\u89c9\u53bb\u4e86\uff0c\u7d2f\u4e86\u3002function [sys,x0,str,ts] = sfungain(t,x,u,flag,gain)switch flag,case 0,sizes = simsizes;sizes.NumContStates = 0;sizes.NumDiscStates = 0;sizes.NumOutputs = 1;sizes.NumInputs = 1;sizes.DirFeedthrough = 1;sizes.NumSampleTimes = 1;sys = simsizes(sizes);x0=[];str=[];ts=[0,0];case 3,sys=gain*u;case {1,2,4,9},sys = [];end\u505a\u597d\u4e86s\u51fd\u6570\u540e\uff0csimulink--user-defined function\u4e0b\u62d6\u4e00\u4e2aS-Function\u5230\u4f60\u7684\u6a21\u578b\uff0c\u5c31\u53ef\u4ee5\u7528\u4e86\uff0c\u5728simulink----user-defined function\u8fd8\u6709\u4e2as-Function Builder\uff0c\u4ed6\u53ef\u4ee5\u751f\u6210\u7528c\u8bed\u8a00\u5199\u7684s\u51fd\u6570\u5728matlab\u7684workspace\u4e0b\u6253sfundemos\uff0c\u53ef\u4ee5\u770b\u5230\u5f88\u591a\u6f14\u793as\u51fd\u6570\u7684\u7a0b\u5e8f\u3002
就这个模型而言，我看不出使用S函数实现有什么好处。
如果用S函数实现，会涉及到一些具体的问题：
1、这些常数是在S函数中直接定义，还是要求可以在外部修改（例如在基本工作区中定义）？
2、是否需要把输入独立出来？mg项与状态无关，原则上可以作为一个输入处理，但也可以直接放在S函数里面。
3、初值是否要求从外部指定？
这几个方面的问题都是可以解决的，但取决于要求高低，实现的复杂程度不一样。
这里姑且按照最简单的情况来处理，即：
1、常数直接在S函数内部定义；
2、把m*g作为系统模型的一部分，不视为输入，而直接放在S函数中；
3、初值直接在S函数中，不从外部指定。
参考代码（只列出修改了的mdlInitializeSizes、mdlDerivatives和mdlOutputs三个函数，其它代码与模板sfuntmpl中的内容完全相同）：
function [sys,x0,str,ts,simStateCompliance]=mdlInitializeSizes
%
% call simsizes for a sizes structure, fill it in and convert it to a
% sizes array.
%
% Note that in this example, the values are hard coded. This is not a
% recommended practice as the characteristics of the block are typically
% defined by the S-function parameters.
%
sizes = simsizes;
sizes.NumContStates = 2;
sizes.NumDiscStates = 0;
sizes.NumOutputs = 1;
sizes.NumInputs = 0;
sizes.DirFeedthrough = 0;
sizes.NumSampleTimes = 1; % at least one sample time is needed
sys = simsizes(sizes);
%
% initialize the initial conditions
%
x0 = [0; 0];
%
% str is always an empty matrix
%
str = [];
%
% initialize the array of sample times
%
ts = [0 0];
% Specify the block simStateCompliance. The allowed values are:
% 'UnknownSimState', < The default setting; warn and assume DefaultSimState
% 'DefaultSimState', < Same sim state as a built-in block
% 'HasNoSimState', < No sim state
% 'DisallowSimState' < Error out when saving or restoring the model sim state
simStateCompliance = 'UnknownSimState';
% end mdlInitializeSizes
function sys=mdlDerivatives(t,x,u)
k=5;
a1=1;
a2=1;
g=10;
m=70;
f = -k*x(1) * (x(1)>0);
sys = [x(2); (m*g+f-a1*x(2)-a2*x(2)*abs(x(2)))/m];
% end mdlDerivatives
function sys=mdlOutputs(t,x,u)
sys = x(1);
% end mdlOutputs
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绛旓細>> f = @(x) sum(cumsum([1:x].^0.5));% 浣跨敤涓句緥>> f(1)ans = 1>> f(2)ans = 3.4142>> f(10)ans = 104.4787
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绛旓細s=0;for n=0:500 s=s+pi^n;end
绛旓細function s=mysum(n)if n==1 s=1;else s=n+mysum(n-1);end 妫楠屾墽琛岀粨鏋滐細>> s=mysum(5)s = 15 >> s=mysum(10)s = 55
绛旓細闂澶锛屽氨涓嶇敤涓涓鎸囨浜嗭紝浠ヤ笅绋嬪簭宸茬粡缁忚繃璋冭瘯鎴愬姛銆俧unction [sys,x0,str,ts] = test_0105(t,x,u,flag)switch flag,case 0,[sys,x0,str,ts]=mdlInitializeSizes;case 3,sys=mdlOutputs(t,x,u);case {2,4,9},sys=[];otherwise error(['Unhandled flag = ',num2str(flag)]);e...
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