Error in while loop

function IsStable(polynomial)
if AllNonZero(polynomial) == false
    H=[]
elseif AllSameSign(polynomial) == false
    H=[]
else 
   HurwitzMatrix(polynomial);
   pm = length(polynomial);                       
        while i=1:pm
        minor(i)=det(polynomial(1:i,1:i));             
        end
            if minor(i)>0
                B=1  
            else
                B=0
            end
end

I am trying to run this code but get this error,

Undefined function or variable 'minor'.

Error in IsStable (line 12)
            if minor(i)>0        

Any suggestions? Thank you.

Answer 1

[Torsten]

Do you want a different value for B for each minor, i.e. B(i) instead of B ?

Then use

function IsStable(polynomial)
if AllNonZero(polynomial) == false
    H = []
elseif AllSameSign(polynomial) == false
    H = []
else 
   HurwitzMatrix(polynomial);
   pm = length(polynomial);                       
   for i = 1:pm
     minor(i) = det(polynomial(1:i,1:i));             
     if minor(i) > 0
       B(i) = 1  
     else
       B(i) = 0
     end
   end
end

[Mughees Asif]

Hi, no i just want the output to be either 1 (if all principle minors are more than 0) and 0 (if all the principle minors are less than 0). When I run your code, I get the following error,

Index in position 1 exceeds array bounds (must not exceed 1).

Error in IsStable (line 10)
     minor(i) = det(polynomial(1:i,1:i));

Thank you.

[Torsten]

function IsStable(polynomial)
if AllNonZero(polynomial) == false
    H = []
elseif AllSameSign(polynomial) == false
    H = []
else 
   HurwitzMatrix(polynomial);
   pm = length(polynomial);                       
   for i = 1:pm
     minor(i) = det(polynomial(1:i,1:i));                  
   end
   B = Inf;
   if minor > 0
     B = 1;
   else if minor < 0
     B = 0;
   end
 end
   

To avoid the error, define the array/matrix "polynomial" you pass to "IsStable" properly.

[Mughees Asif]

This is not for a specific polynomial, it should work forany arbitrary polynomial,

So for example, this is how I call the function in the command window,

>>IsStable([1.0000    1.2000    0.8562    0.3360    0.0321    0.0539])

The input vector can be any arbitrary vector basically. Thank you for the replies.

[Torsten]

And what do you expect polynomial(1:i,1:i) to be for this polynomial ? As defined, your polynomial is a vector, not a matrix.