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From: Rolando on 14 Jun 2010 09:42
I'm trying to differentiate sin(x) based on the iteration loop. But evertime i try to i get this error 'DOUBLE cannot convert the input expression into a double
array'

y=[];
syms x;
f=sin(x);
for i=1:7
% Taylor series of sin(x)
y(i,:)=(-1)^i*(diff(f,i))/(2*i+1);
end
From: Steven Lord on 14 Jun 2010 10:12

"Rolando " <rchacon(a)handson.net> wrote in message
news:hv5bje$1c5$1(a)fred.mathworks.com...
> I'm trying to differentiate sin(x) based on the iteration loop. But
> evertime i try to i get this error 'DOUBLE cannot convert the input
> expression into a double
> array'
> y=[];
> syms x;
> f=sin(x);
> for i=1:7
> % Taylor series of sin(x)
> y(i,:)=(-1)^i*(diff(f,i))/(2*i+1);

In order to store a sym object (which is what the right-hand side is) into a
double array (which is what the subscripted assignment on the left is
attempting to do) MATLAB must convert the sym object into a double array.
Since your right-hand side contains a symbolic variable and you haven't
given that symbolic variable a numeric value, MATLAB cannot perform the
conversion and so (correctly) errors.

Two solutions:

1) Make y a vector of sym objects. If you do this, no conversion will be
needed as the left and right-hand sides will be the same type.

y = sym(zeros(7, 1));
syms x;
f=sin(x);
for i=1:7
% Taylor series of sin(x)
y(i)=(-1)^i*(diff(f,i))/(2*i+1);
end

2) Make your y a cell array. Cell arrays can store any data type, so when
you assign the sym object into the _contents_ of the ith cell in the cell
array, no conversion is needed. [If you attempted to assign into the ith
cell itself using y(i) = ... then MATLAB would attempt to convert the sym
object into a cell itself, which would fail for different reasons.]

y = cell(7, 1);
syms x;
f=sin(x);
for i=1:7
% Taylor series of sin(x)
y{i}=(-1)^i*(diff(f,i))/(2*i+1);
end

--
Steve Lord
slord(a)mathworks.com
comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ
To contact Technical Support use the Contact Us link on
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