taylor series method expansion

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PJS KUMAR
PJS KUMAR on 18 Sep 2018
Edited: Walter Roberson on 19 Sep 2018
I am using the following code for taylor series
function [T,Y] = taylor(f,a,b,ya,m)
h = (b - a)/m;
T = zeros(1,m+1);
Y = zeros(1,m+1);
T(1) = a;
Y(1) = ya;
for j=1:m
tj = T(j);
yj = Y(j);
D = feval('df',tj,yj);
Y(j+1) = yj + h*(D(1)+h*(D(2)/2+h*(D(3)/6+h*D(4)/24)));
T(j+1) = a + h*j;
end
At command prompt i am giving the values as follows and getting error
>> syms x y;
>> f=4*x^3+1
f =
4*x^3 + 1
>> taylor(f,0,1,1.5,4)
Error using sym/taylor (line 99)
The value of 'x' is invalid. It must satisfy the function: @(x)isvector(x)&&isAllVars(x).
  9 Comments
PJS KUMAR
PJS KUMAR on 19 Sep 2018
can we use 'diff' function to assign derivatives to D(1), D(2), D(3) etc.
Walter Roberson
Walter Roberson on 19 Sep 2018
Well you could if you had a variable name to take the derivative with respect to, and you had some reason for D(1) being different from D(2), D(3) etc.

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Answers (1)

Walter Roberson
Walter Roberson on 18 Sep 2018
You are somehow invoking the symbolic toolbox taylor routine instead of your own. Make sure that you match file name with function name and that your path is correct to prioritize your own function.

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