taylor series method expansion

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PJS KUMAR
PJS KUMAR 2018-9-18
编辑： Walter Roberson 2018-9-19
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).
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PJS KUMAR
PJS KUMAR 2018-9-19
can we use 'diff' function to assign derivatives to D(1), D(2), D(3) etc.
Walter Roberson
Walter Roberson 2018-9-19
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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回答（1 个）

Walter Roberson
Walter Roberson 2018-9-18
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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