plotting a polynomial problem

Question

vaggelis vaggelakis 2012-11-28

hello everyone!

maybe it's too simple, but i got a little angry trying to plot a polynomial

let's say : u=a*x+b*x^2+c*x^3+d*x^4 and x=0:0.01:1 when i try to evaluate u the red message says

Error using ==> mpower Matrix must be square.

i had no problem plotting another function like f=a-b*exp(4*x)+c*x

why does the error come up?

(i found something for "polyval" function but how do i use it when i have only x multipliers?)

I can evaluate the polynomial when x has a single value and it is not an array

Answer 1

Azzi Abdelmalek 2012-11-28

编辑：Azzi Abdelmalek 2012-11-28

use operations element by element .^

x=0:0.01:1
u=a*x+b*x.^2+c*x.^3+d*x.^4

because x is a vector, to compute x^2, x must be square. So you can use

[2 4 6].^2=[2^2 4^2 6^2]