Differentiation with str2sym
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Hello,
I am trying to differentiate usinf str2sym but i seem to get some errors.
Here is the code:
clear all
y(1) = str2sym ('x(1)');
y(2) = str2sym ('x(2)');
f = y(1) + y(2);
diff(f, y(1))
This is the error i get
Error using sym/diff (line 70)
Second argument must be a variable or a nonnegative integer specifying the number of
differentiations.
Error in prove (line 8)
diff(f, y(1))
回答（1 个）
Walter Roberson
2020-5-12
The error message is correct. You can only differentiate with respect to an entire variable, not with respect to a function call like x(1)
x = sym('x', [1 2]);
y(1) = str2sym ('x(1)');
y(2) = str2sym ('x(2)');
y = mapSymType(y, 'x', @(e) x(children(e)));
f = y(1) + y(2);
diff(f, y(1))
2 个评论
Gabriele Ansaldo
2020-5-12
Walter Roberson
2020-6-15
x = sym('x', [1 2]);
y(1) = str2sym ('x(1)');
y(2) = str2sym ('x(2)');
Y = mapSymType(y, 'x', @(e) x(children(e)));
f = Y(1)^2 + Y(2);
df = diff(f, Y(1));
df = subs(df, x, y);
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2020-5-11
2020-6-15
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