MATLAB: Indexing polynomials using ‘for’ loop

indexinglooppolynomialspolyval

I need help about an exercise that I've been given from my professor. Six polynomials are given:
  • p1 = [0 2 0 -2 6 -1]; % the first polynomial is p1(x)=2x^4-2x^2+6x-1
  • p2 = [1 3 0 -2 0 0]; % the second polynomial is p2(x)=x^5+3x^4-5x^2
  • p3 = [0 0 3 1 0 -10]; %…
  • p4 = [0 0 0 -4 16 -5]; %…
  • p5 = [1 -1 0 1 0 -1];
  • p6 = [3 -12 0 0 0 7];
Using 'polyval(p(i),2/3)' function I should create new vector 'A' that contains all the values of the polynomials from 'p1' to 'p6'(i=1:6) for x=2/3. Then find the minimum and maximum value of the vector. I want to know how can I loop through the polynomials to find their value and put that value in the new vector. Thank you in advance.

Best Answer

%%Solution 1: (not recommended)
p1 = [0 2 0 -2 6 -1];
p2 = [1 3 0 -2 0 0];
p3 = [0 0 3 1 0 -10];
p4 = [0 0 0 -4 16 -5];
p5 = [1 -1 0 1 0 -1];
p6 = [3 -12 0 0 0 7];
polyValue=zeros(6,1);
for i=1:6
  polyValue(i)=eval(sprintf('polyval(p%d,2/3)',i));
end
fprintf('Solution 1:(not recommended)\nmin: %f, max: %f.\n',min(polyValue),max(polyValue));
%%Solution 2: 
p  = [0 2 0 -2 6 -1; ...
      1 3 0 -2 0 0; ...
      0 0 3 1 0 -10; ... 
      0 0 0 -4 16 -5; ...
      1 -1 0 1 0 -1; ...
      3 -12 0 0 0 7];
polyValue=zeros(6,1);
for i=1:6
  polyValue(i)=polyval(p(i,:),2/3);
end
fprintf('Solution 2:\nmin: %f, max: %f.\n',min(polyValue),max(polyValue));
Once you run it you get this results:
Solution 1:(not recommended)
min: -8.666667, max: 5.024691.
Solution 2:
min: -8.666667, max: 5.024691.
As you can see the difference between the solutions is slightly how the polynomial coefficients are stored.
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