# How to derivate a vector

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Hi, I put a polynom ( x^2+x-1) in a form of a vector :

[1 1 -1].I don't know how to derivate this vector and how to evaluate it.

Thanks, Thierry.

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### Answers (3)

Image Analyst
on 12 Apr 2015

Not sure how those 3 numbers came from that equation, but anyway....The derivative is the slope. You have two line segments, from 1 to 1 and from 1 to -1. So the slope of the first line segment is 0 and the slope of the second line segment is -2. You can get this from

slopes = diff(yourVector);

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Star Strider
on 12 Apr 2015

If you want to evaluate your polynomial and do a numerical derivative, use the polyval function to evaluate it, then the gradient function to take the derivative:

h = 0.1; % Spacing Constant

x = -5:h:5; % Independent Variable Vector

y = polyval([1 1 -1], x); % Evaluate Polynomial

dydx = gradient(y, h); % Take Numerical Derivative At Each Value Of ‘x’

Note that unlike diff, the gradient function will produce a vector the same length as the original data vector.

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Image Analyst
on 12 Apr 2015

Youssef Khmou
on 12 Apr 2015

additionally to the above answers, the simplest way to evaluate the polynomial is via anonymous function :

f=@(x) x.^2+x-1

x=0:0.1:10;

Generally, coefficients vector is used to find the roots. concerning the derivation, gradient is more efficient than diff, when you have the sample rate :

df=gradient(f(x),0.1);

plot(x,f(x),x,df,'r')

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