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[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.

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Giuseppe Dibenedetto
编辑： Walter Roberson 2019-12-3
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?

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