MATLAB: How to extract just one value

polynomialrootsvector

Hi,

suppose I have a polynomial plot and find roots using the "roots" command and i get vector with 2 or more values. How do i just get one particular value out of the 2 or more values?

Thanks

Best Answer

Index it. For example,

r = roots([9, 2, 4, -7]);
disp(r(1))

If you want to look for real roots then

r(imag(r)==0)

will return only real-valued roots

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MATLAB: Select one root of an second degree equation

You could also use the formula for second degree equations. If the equation is:

 a*x^2 + b*x + c = 0

then get the positive root, (if there is just one,) with:

 r = (-b + sign(a)*sqrt(b^2-4*a*c))/(2*a);

MATLAB: Subplot in loop just plotting the first y value

Try this. I haven't tested it, just changed it off the top of my head, but the idea is what you want even if there are a couple of things you need to fix in the code - i.e. get rid of the nested loops and just index into c so that you do 4 different plots.

c=[10,20,40,80]
for n=1:4
    figure(1)
    subplot(1,4,n)
    x=linspace(0,2*pi,c(n));
    y=atan(x);
    plot(y)
end

Edit: I have tested now after a couple of fixes to my original and this seems to work.

Best Answer

Related Solutions

MATLAB: Select one root of an second degree equation

MATLAB: Subplot in loop just plotting the first y value

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