Hello, I would like to ask help to solve the parametric inequality coming out after applying the Routh Hurwitz criterion and plot the the solution as in the picture.

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RICCARDO ZAVADLAL
RICCARDO ZAVADLAL 2023-10-21
回答： Aishwarya 2023-10-31
Ran in:
The problem is that i cannot find a similar command "isolate" for inequalities, i would like to plot the solutions of the variable a,b as in the picture. THe code is the following, i just need a few lines more to complete but i dont have ideas anymore. THanks
clc
clear all
syms a b
D= [1+b+a, 2*(1-b), -a+1+b]; % parametric polynomial (1+b+a)s^2+2*(1-b)*s+-a+1+b
l=length(D)
l = 3
syms m
if mod(l,2)==0
m=sym(zeros(l,l/2));
[cols,rows]=size(m);
for i=1:rows
m(1,i)=D(1,(2*i)-1);
m(2,i)=D(1,(2*i));
end
else
m=sym(zeros(l,(l+1)/2));
[cols,rows]=size(m);
for i=1:rows
m(1,i)=D(1,(2*i)-1);
end
for i=1:((l-1)/2)
m(2,i)=D(1,(2*i));
end
end
for j=3:cols
if m(j-1,1)==0
m(j-1,1)=0.001;
end
for i=1:rows-1
m(j,i)=(-1/m(j-1,1))*det([m(j-2,1) m(j-2,i+1);m(j-1,1) m(j-1,i+1)]);
end
end
disp('--------The Routh-Hurwitz array is:--------'), simplify(m)
--------The Routh-Hurwitz array is:--------
ans = 
% --------------------End of Bulding array--------------------------------
%{
% Checking for sign change
Temp=sign(m);a=0;
for j=1:cols
a=a+Temp(j,1);
end
if a==cols
disp(' ----> System is Stable <----')
else
disp(' ----> System is Unstable <----')
end
%}
h=m(:,1);
for i=1:1:length(h)
isolate(h(i)==0,b)
end
ans = 
ans = 
ans = 

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采纳的回答

Aishwarya
Aishwarya 2023-10-31
Ran in:
Hi,
I understand that you are looking to plot the inequalities obtained through your code in order to resemble the graph shown in the question. After reviewing the above code, I have provided an example code that will plot the inequalities and achieve the desired graph.
a = -5:0.01:5;
b = -5:0.01:5;
% Create 2-D grid coordinates
[A, B] = meshgrid(a,b);
% Create a 2-D grid which satisfy the inequalities
ineq = (B > -A - 1) & (B < 1) & (B > A - 1);
% Plot the points which satisfy equations
ineq = double(ineq);
ineq(ineq==0) = NaN;
h = pcolor(A,B,double(ineq));
h.EdgeColor = 'none';
grid on
Please refer to the MathWorks documentations below for more information about the functions used:
I hope this helps!

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