[error] - Error using sym/subsindex (line 855) Invalid indexing or function definition. Indexing must follow MATLAB indexing. Function arguments must be symbolic variables, and function body must be sym expression.

Hi,

In Matlab I'm trying to differentiate this multivariable eqaution respect to each variable to find minimums.

The code is summarily:

R=sym('R','real');
T_f=sym('T_f','real');
K=sym('K','real');
root_sum_square_diff =
 ((113387136614400/(14796771590290569*K + 805306368000000*R + 429496729600*pi*T_f + 113387136614400) - 917/10)^2 + (7046430720000/(14796771590290569*K + 12582912000000*R + 26843545600*pi*T_f + 7046430720000) - 481/5)^2 + (881810472960/(722498612807157*K + 2516582400000*R + 3355443200*pi*T_f + 881810472960) - 477/5)^2 + (1067030937600/(9912680967714189*K + 1572864000000*R + 5872025600*pi*T_f + 1067030937600) - 468/5)^2 + (859664547840/(3846582614585301*K + 1258291200000*R + 3690987520*pi*T_f + 859664547840) - 477/5)^2 + (2034892800/(34664410983609*K + 3072000000*R + 13926400*pi*T_f + 2034892800) - 458/5)^2)^(1/2)

when I launch the command:

 diff(root_sum_square_diff,R)

I obtain this 2 errors:

Error using sym/subsindex (line 855)

Invalid indexing or function definition. Indexing must follow MATLAB indexing. Function arguments must be symbolic

variables, and function body must be sym expression.

Error in sym/subsref (line 900)

R_tilde = builtin('subsref',L_tilde,Idx);

Anybody can hel me? There's any other command I can use?

[Sebastian Benecke]

I don't get any errors running your code.

[Giuseppe Dibenedetto]

Actually I tried copying the instruction i wrote here and I have any problem too.

But when I launch the full code that provice me the function "sum_root_square_diff" the error came up.

Solved anyway