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### Highlights from Find Polynomial Intersections

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# Find Polynomial Intersections

### Alister Fong (view profile)

19 Dec 2003 (Updated )

Find the intersections between 2 or more polynomials.

File Information
Description

Given the coefficients of 2 or more polynomials, this program will return their intersection points be it real or imaginary and the full string representation of these polynomial equations. e.g. 'y=2*x^3+4*x^2+3'
Suitable for use with the MATLAB 'polyfit' function

MATLAB release MATLAB 6.0 (R12)
08 Sep 2011 Lufuno Vhengani

### Lufuno Vhengani (view profile)

This is nice, I used it first time and it worked.

02 Jul 2009 Edward

### Edward (view profile)

I can't get this code to work, I have solve() but I get an error even when using the supplied test function:

======================================================
Randomly generating coefficient values based on constraints
======================================================
-5
5 -3
======================================================
Solve the two polynomials using "solve_polynomials"
======================================================
??? Error using ==> str2num at 33
Requires string or character array input.

Error in ==> solve_polynomials at 115
intersection_coords = [intersection_coords; str2num(X(n).s),str2num(Y(n).s)];

Error in ==> test_solve_polynomials at 99
[intersection,real_intersection,complex_intersection,polystr] = ...

It would help me out a lot if it worked tho!

cheers

ed

Comment only
07 May 2004 Andrea Johnson

Acutally, solve is part of the symbolic math toolbox which is not part of the core matlab package, I am unable to use this function as well...the alternate solution suggested would work for the intersection of two vectors (as would the function intersect), but not a poly structure, which just consists of the coefficients

11 Feb 2004 Alister Fong

For your information, 'solve' is a built-in matlab function. Please check the matlab documentations.

Comment only
07 Feb 2004 Duane Hanselman

this function calls an unknown function named "solve", which renders this function unusable.
This function creates a string representation of the input polynomial row vectors.

For two polys can't this function be replaced by:

function x=polyintersect(p1,p2)
np1=length(p1);
np2=length(p2);
p=[zeros(1,np2-np1) p1]-[zeros(1,np1-np2) p2]; % find polynomial difference
x=roots(p); % zeros of difference are intersections????