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

Answer 1

[Paulo Silva]

 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

[sadel]

I have a diplay panel which displays strings like 'Plant:' and transfer functions. I use the evalc to convert handles.PID_sys to string. After this, I use strvcat to connect the string 'Plant:' and the string of the transfer function. Then , I display them on an editbox.

[sadel]

I need the s symbol.

[Paulo Silva]

So does my code solve your problem or not?

[sadel]

Yeah, thank you!!!!

[sadel]

but now there is another problem. I cannot execute the 'c2d' function with this transfer function handles.PID_sys=1 and I think because this isn't a transfer function.

[sadel]

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

[Paulo Silva]

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

Answer 2

[Walter Roberson]

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

[Paulo Silva]

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.