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# How can we compute the derivative of polynomials?

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Omar B. on 1 Oct 2020
Closed: MATLAB Answer Bot on 20 Aug 2021
How can we compute the derivative of the (m-1) polynomials at a point?
I got the following error:
The following error occurred converting from sym to double:
Unable to convert expression into double array.
Error in untitled (line 42)
p(1)=((x-alpha(1))*p0)/beta(1);
syms x
p0=1;
x0=2;
p(1)=((x-.2)*p0)/.3;
p(2)=((x-.5)*p(1)-.3*p0)/1.3;
dp(1)=eval((subs(diff(p(1),x,1),x,x0)) )
dp(2)=eval((subs(diff(p(2),x,1),x,x0)) )
for j=3:m-1
p(j)=((x-.2)*p(j-1) - .3*p(j-2))/1.3;
dp(j)=eval((subs(diff(p(j),x,1),x,x0)));
end
Omar B. on 2 Oct 2020
yes, I got the same results. Thank you so much

David Hill on 1 Oct 2020
Why not just use polynomial representation
p = [3 0 -2 0 1 5];
pd=polyder(p);
x=1:10;
val=polyval(pd,x);
##### 2 CommentsShowHide 1 older comment
Walter Roberson on 2 Oct 2020
The coedfficients would be in pd

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