POLYVAL Evaluate Polynomial Fit at Selected Points

Usage

The polyval routine has the following syntax

  y = polyval(p,x)

where p is a vector of polynomial coefficients, in decreasing degree (as generated by polyfit, for example). If x is a matrix, the polynomial is evaluated in the matrix sense (in which case x must be square).

Function Internals

The polynomial is evaluated using a recursion method. If the polynomial is

$$p(x) = p_1 x^n + p_2 x^{n-1} + \dots + p_n x + p_{n+1}$$

then the calculation is performed as

$$p(x) = ((p_1) x + p_2) x + p_3$$

Example

Here is a plot of x^3 generated using polyval

--> p = [1 0 0 0]
p = 
  <int32>  - size: [1 4]
 
Columns 1 to 4
             1              0              0              0  
--> x = linspace(-1,1);
--> y = polyval(p,x);
--> plot(x,y,'r-')

Here is the resulting plot