How can I turn s/s to 1?

Question

sadel 2011-6-8

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/9049-how-can-i-turn-s-s-to-1

I run this code and if I click yes without change anything in the inputdlg, I receive 's/s'. How can I return this to '1' in this situation?

 prompt={'Proportional Coefficient Input','Integral Coefficient Input','Derivative Coefficient Input'};
defans={'1','0','0'};
answer=inputdlg(prompt,'PID Coefficient Input',1,defans,'on');
if (~isempty(answer))
    if (~isempty(answer{1}))&(~isempty(answer{2}))&(~isempty(answer{3}))&(answer{1}~='0')
        syms s 
        x1=str2num(answer{1});
        x2=str2num(answer{2});
        x3=str2num(answer{3});  
        handles.pid(1)=x1(1);
        handles.pid(2)=x2(1);
        handles.pid(3)=x3(1);
        handles.PID_num=[handles.pid(3),handles.pid(1),handles.pid(2)];
        handles.PID_den=[1,0];
        handles.PID_sys=tf(handles.PID_num,handles.PID_den);
        evalc('handles.PID_sys')
end 
end

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Answer 1

Paulo Silva 2011-6-8

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/9049-how-can-i-turn-s-s-to-1#answer_12448

在 MATLAB Online 中打开

 prompt={'Proportional Coefficient Input','Integral Coefficient Input','Derivative Coefficient Input'};
defans={'1','0','0'};
answer=inputdlg(prompt,'PID Coefficient Input',1,defans,'on');
if (~isempty(answer))
    if (~isempty(answer{1}))&(~isempty(answer{2}))&(~isempty(answer{3}))&(answer{1}~='0')
        syms s 
        x1=str2num(answer{1});
        x2=str2num(answer{2});
        x3=str2num(answer{3});  
        handles.pid(1)=x1(1);
        handles.pid(2)=x2(1);
        handles.pid(3)=x3(1);
        handles.PID_num=[handles.pid(3),handles.pid(1),handles.pid(2)];
        handles.PID_den=[1,0];
        handles.PID_sys=tf(handles.PID_num,handles.PID_den);
        [num,den] = tfdata(handles.PID_sys);
        if(num{:}==den{:})
        handles.PID_sys=1;
        end
        evalc('handles.PID_sys') 
end 
end

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sadel 2011-6-8

with this handles.PID_sys=tf([1],[1]); instead of this handles.PID_sys=1 is better!!! :)

Paulo Silva 2011-6-8

even better -> handles.PID_sys=tf(1);

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Answer 2

Walter Roberson 2011-6-8

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/9049-how-can-i-turn-s-s-to-1#answer_12458

s/s is not generally 1. In particular, that fails for 0, infinity, -infinity, and NaN.

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Paulo Silva 2011-6-8

that's why the tf leaves the results the way it does, I never seen the s/s situation before, always had transfer functions with more poles than zeros, sometimes it's good to be here trying to help others, we always learn new things.

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