Error evaluating symbolic expressions with symbolic arrays.

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pefernan
pefernan 2017-4-19
回答： Walter Roberson 2017-4-19
I get an error when I run this code (R2017a):
x = sym('x',[1 3]);
y = x(1) + x(2) + x(3);
x(1)=1;
x(2)=1;
x(3)=1;
double(subs(y))
If instead of an array of syms I use separate syms variables, the code runs with no errors. This is the error I get:
Error using symengine
DOUBLE cannot convert the input expression into a double array.
Error in sym/double (line 643)
Xstr = mupadmex('symobj::double', S.s, 0);
How can I fix this mantaining the array of syms? It would be great to keep the array as I need to use large arrays of syms.

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采纳的回答

Walter Roberson
Walter Roberson 2017-4-19
x(1)=1; does not set x1 to 1: it changes the vector x to [1, x2, x3]
Instead,
X = [1, 1, 1];
subs(y, x, X)

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