# Roots in Matlab

1. Sep 17, 2011

Dear Fellow,

I need to find the roots of equation
x^8- 2x^6+3x^4-7x^2+a=0
in MATLAB, in such a way that I need 4 non repeating roots.

I have used the technique of
p=[1 -2 3 -7 1]
s=roots(p)
x1=s(1)
x2=s(2)
x3=s(3)
x4=s(4)
where xi,i=1,2,3,4 are roots of the above equation,

2nd option my friend gave me is

p=[1 -2 3 -7 1]
s=sqrt(roots(p))
x1=s(1)
x2=s(2)
x3=s(3)
x4=s(4)
this will again give me four roots of the equation,

need your help to find the four roots of above equation.

Regards

2. Sep 17, 2011

### uart

Clearly your polynomial is in x^2, so your friends solution is the correct one. Though you should of course use the plus and minus (+/-) of the roots.

3. Sep 17, 2011

Okay ,,,, thanks uart,, thats really help full

4. Sep 18, 2011

can you please give my any idea how to define vertical axis in matlab plot command

thanks

5. Sep 18, 2011

### Pythagorean

it's automatically designated by your data set, but you can also set particular properties of the axis with (for example):

set(gca,'YTick',[0 0.05 0.075 0.1 0.15 0.2 0.25])

and you could even go as far as to label each of the points:

set(gca,'YTickLabel','0|0.05|Cutoff|0.1|0.15|0.2|0.25')

full documentation:
http://www.mathworks.com/help/techdoc/creating_plots/f1-19798.html [Broken]

Last edited by a moderator: May 5, 2017