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How can we compute the derivative of polynomials?

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Omar B.
Omar B. 2020-10-1
关闭： MATLAB Answer Bot 2021-8-20
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
  11 个评论
显示 9更早的评论
James Tursa
James Tursa 2020-10-2
Both eval( ) and double( ) work for me with your example code. What is your actual code?

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回答（1 个）

David Hill
David Hill 2020-10-1
Why not just use polynomial representation
p = [3 0 -2 0 1 5];
pd=polyder(p);
x=1:10;
val=polyval(pd,x);
  2 个评论
Omar B.
Omar B. 2020-10-1
I just here wrote an example , but I need to refer the coefficients to another code. Is there another way?

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