how do i find the intersections between two functions ?

i try to find how is the code for intersections between two functions ( with ''if'') plz ..i need help!

[the cyclist]

This is not twitter. Please feel free to use more than 140 characters to give a more complete explanation of your problem. You have not given us close to enough information to help you.

[maria_maths_]

i try to find the code for intersections between two functions ( i need price of x and y ) without using the 'fzero' . Can i do it with''if''? for example . if i have :

a=[31 23 65 8]
b=[4 56 8 10 ]
c=[21 45 90 6]
plot(a,b)
hold on
plot(c,b)

can i find the A(xa,ya) , B (xb,yb)... which A and B is the common prices of the two plots ??? thanksss

[Walter Roberson]

Which of the 6 intersection points did you want?? I have put arrows and numbered them so that we can be sure that we are talking about the same intersections.

If you do not want all of these, then how are you selecting which ones you want?

Do you need them in a particular order?

[maria_maths_]

1)i want all of this !can i do it ? 2) can i mark all the intersections with red colour to find it easier in the plot ? whats the code of this ?

Answer 1

[Walter Roberson]

It has been proven that there cannot be any finite algorithm which can give you all of the intersections of two infinite functions (that does not mean that the functions have to be defined at infinity: it also covers continuous functions on a line segment, and covers functions of infinite subsets of the integers.)

For example let one of the functions be the Riemann Zeta function, and let the other function be the constant 0. If there were a finite algorithm that could find the intersections of any two infinite functions then you could apply that finite algorithm to find all the places where the Riemann Zeta function is 0. There is no known way to find all of the zeros of the Riemann Zeta function; any algorithm for doing so would give an answer to the Riemann Conjecture.

[Walter Roberson]

http://www.mathworks.com/matlabcentral/fileexchange/22441-curve-intersections looks like a possibility for your purposes.