MATLAB Answers


How do I differentiate this function?

Asked by Leandro Nitsch on 26 Mar 2019
Latest activity Commented on by Torsten
on 27 Mar 2019
Hi guys,
I am new to MATLAB and have the following problem: I programmed the following function
I took derivatives by hand but then I wanted MATLAB to take the derivatives for me with respect to independent variables K, NRC, X, R and NRM. Somehow I always get the following error message when using the diff function:
Error using sym/subsindex (line 769)
Invalid indexing or function definition. When defining a function, ensure that the arguments are symbolic
variables and the body of the function is a SYM expression. When indexing, the input must be numeric,
logical, or ':'.
Error in
Error in sym>funchandle2ref (line 1308)
S = x(S{:});
Error in sym>tomupad (line 1206)
x = funchandle2ref(x);
Error in sym (line 179)
S.s = tomupad(x);
Error in sym/privResolveArgs (line 921)
argout{k} = sym(arg);
Error in sym/diff (line 21)
args = privResolveArgs(S,varargin{:});
By the way my code is the following:
>> gamma=0.3;
syms K NRC NRM R X
Y=@(K,NRC,NRM,R,X) Z*K^gamma((1-eta)*((1-alpha)*NRC^{EOS1}+alpha*(X^v+R^v)^{EOS1/v})^{EOS2/EOS1}+eta*NRM^{EOS2})^{(1-gamma)/EOS2};
partial1 = diff(Y,K);
What am I doing wrong?
Thanks for your answer!


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1 Answer

Answer by Torsten
on 26 Mar 2019
 Accepted Answer

syms Z K gamma eta alpha NRC EOS1 v X R EOS2 NRM
Y= Z*K^gamma*((1-eta)*((1-alpha)*NRC^EOS1+alpha*(X^v+R^v)^(EOS1/v))^(EOS2/EOS1)+eta*NRM^(EOS2))^((1-gamma)/EOS2);
dYdK = diff(Y,K)


Hi Torsten,
Thank you for your anwer. I did what you suggested but am still getting the same error message :/
For me, the code as written works.

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