Substituting a syms variable with another syms variable equation

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Philosophaie
Philosophaie 2013-6-29
Error code:
??? Subscript indices must either be real positive integers or logicals.
Error in ==> EigenValuesVectors4x4ToTensorFactor at 10
f=sym(zeros(4,4,4))
Code:
syms T11 T12 T13 T14 T21 T22 T23 T24 T31 T32 T33 T34 T41 T42 T43 T44
f=sym(zeros(4,4,4))
%MatLab does not like the substitution of a syms variable with another syms variable equation. Is there any way around this?
%h(i,k) is a 4x4 matrix with syms formula in each cell
ta13=solve(h(1,3),'T14')
ta14=solve(h(1,4),'T14')
tb11=subs(h(1,1),'T14',ta14)
tb12=subs(h(1,2),'T14',ta14)

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回答（2 个）

Philosophaie
Philosophaie 2013-6-29
No the "sym" in "f=sym(zeros(4,4,4))" creates "f" as a symbolic zero matrix.
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Walter Roberson
Walter Roberson 2013-6-29
It cannot both create "f" as a symbolic matrix and complain about a subscript.
Your posted error message refers to line 10, but the "f=" line it is complaining about is at most line 3. What is before that in the code ?

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Walter Roberson
Walter Roberson 2013-6-30
Please post the result of
which sym
class(sym) %might generate error message
Also, what does
sym('abc')
return?

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